STOP 1.  Hyde Heritage Rail Trail County Park Exposure

Harpers Formation phyllite and quartzite

Located between Hyde and INdian Rock Dam Rock, Spreing Garden Township

1. Harpers Formation derived from Harpers Ferry, WV
2. Southern 33% of YorkCounty is composed of metamorphic rocks
3. This ridge (Country Club Ridge) is just south of the dividing line between the Piedmont Lowlands Section (PLS) and the Piedmont Uplands Section (PUS).
4. Walk a portion of the exposure and notice what appears to be layering.  Actually this rock has undergone heat and pressure where bedding has become obscure.
5. What you believe is layering is known as foliation – a feature only found in metamorphic rocks where platy minerals in the rock align themselves to produce a flat plane.
6. Notice any folding in the exposure?
7. We are situated very close to a north-south fault.  Although most of the rocks in the PUS are folded, these rocks have been more tightly folded with the influence of the fault.
8. Find isolated beds of quartzite.  Quartztite is thicker “bedded” than the phyllite and more resistant to erosion.
9. There are small quartz veins also found here.
10. Notice how some of the tree roots anchor themselves into the bedrock and are accelerators in weathering of the rock.

Folding in the metamorphic rocks at Hyde

STOP 2.  Stoney Brook Diabase Dike

Diabase and Conestoga Formation limestone

Along the Railroad just west of the Pleasant Acres Road, Springettysbury Township

1. Diabase is an intrusive igneous rock giving the rock a coarse-grained appearance.
2. All diabase in Pennsylvania is Jurassic in age.
3. A dike is a narrow intrusion of magma in this case only measuring about 20 feet wide, but is about 35 miles in length
4. This magma was believed to be about 1100º C. and baked the surrounding rock into a metamorphic rock named as a hornfels.
5. Larger intrusions have formed mineral resources in southeastern Pennsylvania such as the Cornwall Iron Mines, LebanonCounty and Dillsburg magnetite deposit, York       County.
6. The magma intruded the Conestoga Formation composed of limestone.
7. Ripple marks have been found in this thinly-bedded limestone.
8. What is the direction and angle of dip of the limestone?
9. The Conestoga Formation is one of several limestone/dolomite units in the YorkValley, all forming on a continental shelf off the coast of ancient North America known as        Laurentia.
10. This limestone is now considered Cambro-Ordovician in age.

Stoney Brook Dike just west of Pleasant Acres Road

STOP 3.  Accomac Metabasalt

Catoctin Formation

Located along the south side of Accomac Road just west of the intersection with River Road, Hellam Township

1. Formed as a result of rifting of the supercontinent Rodinia about 620 mya.
2. Basalt forms on an oceanic crust (i.e. mid-oceanic ridge)
3. Look for quartz pods (filled-in gas bubbles) sometimes showing a trace of copper
4. Grass-green mineral is epidote and darker green mineral is chlorite
5. Notice crystal size – extrusive meaning it cooled quickly and is fine-grained
6. Fractures in the rock are known as joints (fractures where no movement has taken place)  Geologists can take measurements of joints and calculate direction of pressures
7. Notice one area where bedrock is missing with a small drainage ditch – a possible fault?
8. Across the road notice the erosion taking place as the stream crosses over the bedrock
9. The rock has gone at least one period of heat and pressure – metamorphism (meta)
10. Potholes are well developed in the metabasalt

Accomac road cut exposing the Catoctin metabasalt

STOP 4. Rocky RidgeCountyPark

Chickies Formation – Hellam Member

Located at the end of Deininger Road, Spring Gettysbury Township.  Proceed to the Oak Timbers North Overlook

1. Rock containing rounded pebbles is known as a conglomerate
2. Rock fragments of mostly quartz with occasionally darker fragment of metarhyolite
3. Can you detect any bedding?
4. Notice how the fragments are more resistant to erosion – standing higher than rock
5. Any theories on how this rock formed (include a continental shelf, IapetusOcean and other bodies of water in your thinking)
6. York, Lancaster, Lebanon and Berks counties can be seen from the overlook
7. Can you recognize any familiar landmarks?
8. Harder rocks underlie ridges and softer rocks underlie the valleys, i.e. sandstone and quartzite ridges; limestone and shales in the valleys)
9. We are at an elevation of about 940 feet above sea level
10. We can see a distance of 52 miles to the northeast on a clear day

Hellam Conglomerate exposed at Rocky Ridge County Park.

STOP 5. Sheep Bridge Road

Gettysburg Formation shale and sandstone

Located on the west side of Sheep Rock Road just north of the Conowego Creek, Newberry Township

1. Sandstone has thick bedding and shale has thin bedding. Grain size also varies.
2. Which of the two rocks is more resistant to erosion?
3. These rocks were laid down in an “Everglades” environment as Pangaea was rifting apart
4. Fossils in the area include petrified wood, ferns, dinosaur footprints and reptilian remains
5. The thickness of the New Oxford and Gettysburg formations are at least 25,000 feet thick
6. Can you detect the angle of dip and direction?
7. These rocks are undeformed and positioned nearly the same as when they were deposited
8. The red color of the rock was created when the sediment was above water level and exposed to the atmosphere
9. Clam shrimp found in this formation in DauphinCounty indicates fresh water environment
10. Which layer in this road cut is the oldest?

Sheep Bridge road cut exposing Triassic sedimentary rocks

STOP 6. Pinchot State Park Toboggan Run Area

Diabase Exposure

Warrington Township

1. This is one of the best exposures of diabase in YorkCounty
2. Compare this diabase with that seen at Stoney Brook
3. This diabase formed in a sill (a lenticular body of magma) formed at least one mile beneath the surface
4. In a sill, the magma closest to the outside will cool quicker than the middle
5. This event was the last stage of the rifting of Pangaea
6. Igneous rocks weather in a characteristic rounded shape boulders (spheroidal weathering)
7. Notice the cracks on the rocks – these are believed to be cooling cracks as the magma cooled now magnified by weathering
8. One could have fun here recreating how the boulders were all connected at one time
9. The rock develops a reddish-brown weathering rind
10. How do you think this rock would be for having a good groundwater supply?

Diabase exposed at Toboggan Run at Pinchot State Park

STOP 7.  Rossville   Road Cut

Diabase and Gettysburg Formation hornfels

Located on the east side of Old York Road, 0.50 and 0.75 miles north of Rossville, Warrington Township

1. Check the diabase at the lower road cut for grain size – positioned in the middle or on the edge of the sill?
2. White veins in the diabase of composed of a mineral group known as zeolites.  Heulandite and stilbite are present here in crystals
3. In the upper road cut, this rock was originally rocks similar to what we saw at Sheep Rock Road but these have been heated by the magma now known as hornfels
4. Can you detect the direction of the bedding?
5. A chemical reaction here formed a small amount of native copper to form in the rock
6. Upon weathering of the rock, native copper will adjust to the new conditions forming azurite (blue and malachite (green)
7. This rock has no economic value and only occurs on the joint surfaces
8. Other minerals formed in this method include garnets and opal
9. Gold is found in area streams, mostly washing out of the diabase
10. Collect your pieces of samples for the coffee table!

Azurite and malachite exposed in the upper road cut along Old York Road

I was thinking about doing a blog on several local fossil locations, but I was going to hold off on that until early spring.  However, one of our readers requested some information about fossil collecting and so here we go.  Fossil collecting is rather exciting.  Traveling to a fossil site you are full of anticipation, anxious to get out and hit some rocks and hoping, just hoping, to find something really cool!   Yes, it is cool when you hit the rock in the correct manner, it splits about in its layers and wow, there is a sea shell looking right back at you.  If you are lucky, you will even have two halves of the fossil – the cast and the mold and you can even put the rock back together like no one ever harmed it.  What I think is really neat other than finding something, is that you are the first person to ever see that fossil.  Certainly, since humans weren’t around when these organisms lived in the ocean, you are the first intelligent life to see the animal – period.

A group of fossil nuts collect at Swatara State Park.

Much like mineral collecting, some of the sites are on private property.  By reading this blog doesn’t give you permission to access the land, but I have talked with two owners involved here and the last I knew, they did not mind fossil collectors tearing up their rocks.  Things do change over time and respect a owner’s wished should the area be closed to collectors.

Let’s start in York and Lancaster counties.  Unless you have done some reading of older geologic publications or visited a local museum that had a fossil display, you are probably not aware of many fossil sites right here under your feet.  The reason being is that most of our rocks in the southern half of YorkCounty and the southern two-thirds of Lancaster county are ancient rocks, reflecting a history that went back to 500-600 million years ago.  Yes, we were mostly under an ocean at that span of time.  According to the fossil record, life in the ocean was very sparse, not flourishing with many species.  Oddly enough, even with the limited species, one of the most complex organisms to live in prehistoric seas were trilobites.  Trilobites of the Cambrian age actually lived right here.  At least three species of trilobites have been identified from the York and Lancaster areas, mostly confined to a shale and limestone rock unit known as the Kinzer formation.  In fact, the NorthMuseum in Lancaster has specimens of trilobites collected from a site now destroyed that have only been found there.

Before, I give you several of my favorite sites for these ancient bottom dwellers and king of the ocean, one important fact.   As stated above, live was sparse and this means that finding a trilobite may be a long and patient task.  Don’t expect to find a trilobite in every rock or even two in one day.  But when you find a trilobite, it will be a find that you will not forget.  Going to my later several sites outside of southeastern Pennsylvania will be much more rewarding as those rocks are much younger and formed during a time that life in the ocean was near its peak.

Ollenelus trilobite found at Locust Lane

For YorkCounty fossil seekers, the Locust Lane site has been the best recently exposed.  This roadcut is found in ManchesterTownship just west of Interstate 83.  In fact, there is a Locust Lane underpass on the interstate.  You may access Locust Lane either off the Susquehanna Trail or off of North George Street.  This shale outcrop has produced several specimens of Ollenelus trilobites.  Often times, seeing a fossil in “fresh” rock is difficult.  I once knew a collector who would go to a site, dig up some new rock and let it sit on the surface for several months to weather, which would allow the fossils to be more easily seen.  It was at the Locust Lane site where a gentleman was having a bad day and decided to take a walk to think about his problems.  He sat down on the concrete culvert at this site and while thinking, started to pick up pieces of rock and looking at them.  What did he expect to find, probably nothing, but it was the movement that helped to relax him.  Guess what?  In one of those pieces he found a trilobite (missing its trail and section of body) but it was well preserved.  Now talking about a change of luck, you can imagine his feelings then!!

The KInzer shale exposed at the Locust Lane site

Another roadcut site located in Manchester township is along Bull Road about 0.3 mile north of Greenbriar   Road.  Located on a curve of the road (use much caution here) is a small outcrop of the tan-to-light green shale.  Within this rock, small trilobites have been found and were thought that these were immature ones.  Don’t be surprised to find fragments of a trilobite likes heads or tails.  Often, you will find pieces of fossils rather than the complete animal.

One more site where I never had any luck but trilobites were found in the early 1900’s is in a rather long exposure of the Kinzer shale along North George Street between U.S. Rte. 30 and Interstate 83.  I stop here occasionally to examine rock that may have fallen down during the winter or after the spring thaw.  Maybe, just maybe I would strike it lucky one time to see a freshly exposed trilobite.

In LancasterCounty, the site of the MontessoriAcademy on Weaver   Road in ManheimTownship has yielded some nice fossils.  During the building of the school, fossils were collected and then presented to the academy for a showcase in their lobby.  A cultivated field located just to the north of the school, which they own, has yielded trilobites.  The best time to seek permission from the school would be during the non-productive period with the crops.  Even if not granted permission to collect, check out the showcase of fossils.

Many Cambrian sites in York and Lancaster counties have been  uncovered in the past 20 years with construction.  As rock is dug up by a contractor, especially in the area containing sedimentary rocks including the Kinzer formation, fossil collectors have found some niffy finds.  As with development, there sites are gone in matter of a short period of time.  It doesn’t hurt to keep your eyes open around such projects.

The Roth Road pit in 2010

Perry County is one of the most fossiliferous areas in eastern Pennsylvania.  IT contains a number of rock formations within the Appalachian Mountains that were formed during the Devonian Period, when the sea life was nearly to its peak with species and abundance.  Chances are in many roadcuts or locations where the rock is being removed, you may find fossils.  One such locality that I have been using for an educational stop fro many years is located along Roth Road, about 0.75 mile south of New Bloomfield.  The side of the hill has been dug into removing shale and exposing a number of good fossil beds.    Depending upon how much material and how often the rock is being dug can vary.  Obviously, with more digging, it exposes new rocks for a collector to go through.  Watch this shale though, it is very fragile and can crumble in your hand easily.  It is better to bring home larger pieces and break them down into smaller specimens under a more controlled environment.  What is found here?  Greenops and Phacops (our state fossil) trilobites, a number of clam and brachiopod shells, coral, bryzoan, gastropod and crinoid stems.

A shell found at Swatara State Park, similar to what you will find in Perry County

The second site to bring to your attention is a rather new discovery.  Found in the same rock formation as the Roth Road site in PerryCounty, this site provides good collecting for the smaller children.  It is located about 2 miles west of Auburn, SchulykillCounty along Pa. Rte. 895.  SouthManheimTownship has developed a large area where shale was dug out of the hillside.  If you look in the rock piles close to their maintenance shed, you will find layers that are filled with assorted fossils and jumbled up.  Many of the fossils are broken and appear that the animals were tossed around in the ocean.  Shell fragments, many crinoids and bryzoan dominant this rock.   It reminds me of a low-tide line along the shore.  I have found some nice shells impressions in this area.

Bryzoan found near Auburn

Crinoid stems and shell fragments from Auburn

At first look up higher on the gentle slope of this shale pit, it appears there aren’t many fossils exposed.  I first thought that and suddenly I found a dark-gray hard shale containing rolled-up Phacops trilobites.  Wow, really interesting as this new color of the rock indicates a different environment than that rock found on the bottom.  Pay attention to the harder, darker shale, it contains trilobites that weren’t found in the low tidal rock.

Rounded-up Phacops trilobite – Pennsylvania’s state fossil

Where ever you go fossil collecting, take along a masons hammer with a chisel blade, a chisel for splitting the rock in the layers and possibly a mini sledge to break the larger rocks.  It is advisable to take a box or bucket and newspaper to wrap and pack your finds.  These will be the oldest antiques you will ever find – take care of them.

Coral fossil collected from Swatara State Park but similar specimens can be found in Perry and Schulykill counties

We all have taken walks in the woods or down to our favorite stream and have picked up rocks for the fun of it.  How about going to one of the area lakes or ponds, finding a flat rock and send it flying across the water seeing how many times it skipped to the other side.  Or have you made it a tradition to collect a rock sample from every place you have vacationed?  In some cases, this is not a good idea as it is against the rules to remove and natural resources from that property.  WE all have collected a pile of “pet rocks” but really other than being attractive with its color, how much do you know about rocks?

Are you ready for rock science 101?   Let me spend alittle bit of time in this blog to look at some different rocks, some of which look similar, but I will explain just how different they really are.  Go back to your school days when you sat through a boring earth science class or your elementary school teacher spent a week talking about the earth.  There are two classes of rocks found on Earth: sedimentary, igneous and metamorphic rocks.  Sedimentary rocks are the most common types found on the surface of the Earth.  These rocks were formed from usually some sort of water environment or possibly wind.  They are layered, either with thin layers or thick beds and can be any color.  Examples of sedimentary rocks include sandstone, limestone, shale, conglomerate and breccia.

Igneous rocks are the most common rock within the Earth’s crust.  At one time magma or lava, these rocks are usually massive looking and are dense (heavy).  There is usually no layering present and the color can vary from a light pink to black.  Some igneous rocks contain obvious crystals interlaced together while maybe some igneous rocks contain only very small crystals, not detected by the eye.  Examples of igneous rocks are granite, basalt, rhyolite and diabase.

Metamorphic rocks is the class that many people forget about.  They are the least common in the Earth’s crust and were originally sedimentary or igneous.  Movement within the crust or deep burial of the rocks placed heat and/or pressure on them and changed either the mineral composition or texture, changing it into a new distinct rock type.  These rock can vary in color and sometimes contain abundant mica that makes the rock shiny.  Often, the rock appears to be layered, but be carefully.  As a rock goes through the change of rock, the minerals align themselves perpendicular to the direction of the pressure, thus forming what geologists know as foliation.  Think about the rock known as slate.  Slate has perfect foliation giving it the smooth surface on which to write on.  Other metamorphic rocks include schist, phyllite, quartzite and marble.

As in anything having to do with nature, even the formation of rocks occurs in a cycle.  I challenge many people each year to think about something in nature that isn’t in a cycle.  I have never been challenged with any ideas..  Take for example, the rock cycle.  The cycle starts with magma (what we think the Earth was in its very early stages of life).  When magma cools it forms an igneous rock.  If an igneous rock is exposed to the atmosphere, it is weathered and slowly broken into small pieces known as sediment.  Eventually, the sediment gets washed into a stream or larger body of water.  Mother Nature may use natural glue (minerals) to cement the sediment together that forms sedimentary rocks.  If we place heat and/or pressure on a sedimentary rock, we can form a metamorphic rock.  So much pressure can be placed on a particular rock that the rock will melt back into magma (or the top of our cycle).  Several subcycles within the big cycle can occur.  For example, a sedimentary or metamorphic rock can be weathered and turned into sediment.  Igneous rocks can go directly into a metamorphic rocks when conditions permit, skipping the sedimentary rock stage.  Actually, metamorphic rocks can get re-metamorphosed again without going back to the sediment stage.

The Rock Cycle

Let’s show you pictures of different rocks that at first look identical, but on closer inspection, there is a difference.  The difference in the rocks is the shape of the rock fragments.  The first rock has rounded fragments mostly made up of quartz.  These pebbles have been moved by running water for quite a distance and finally laid down in sand and cemented together by silica.  This rock is known as a conglomerate (sedimentary) and is the rock seen as RockyRidgeCountyPark.  The rock formed within a river channel or in a delta environment.  With quartz being durable, it took a lot of churning of the fragments in water to become this rounded.

Conglomerate found at Rocky Ridge County Park

The second rock has fragment that are angular and appear not to have been transported in water very long.  This rock is known as a breccia since it contains angular fragments. Just like conglomerate, it does not matter what composition the fragments area, if they are rounded the rock is a conglomerate and a breccia if angular.  This breccia is found along Pa. Rte. 194 at the intersection of Maple Grove Road south of Abbottstown.  The rock can also be seen along Old Stage Road northeast of Lisburn in the northern end of YorkCounty.

Breccia from Rte. 194 containing angular fragments

Our second comparison are two igneous rocks.  The first is known as rhyolite, which was once lava that solidified into a rock.  The lines passing through the rock are known as flow lines and represent individual lava flows.  This rock is common in SouthMountain, particularly in the CaledoniaState Park area.  Rhyolite has the same composition as granite, the only difference the rhyolite cooled on the surface rather quickly (relatively speaking) and formed very small crystals.  Granite cooled deep inside the Earth, meaning slower cooling thus forming larger crystals.

Rhyolite from South Mountain

The next rock is known as diabase and is common in the northern portion of YorkCounty.  All of the ridges and hills in the Rossville-Dillsburg-Grantham area consist of this igneous rock.  If you find a sample of diabase at Ski Roundtop or in the roadcut just north of Rossville along Old York Road, you can see small crystals.  Diabase, like granite, cooled beneath the Earth’s surface, forming larger crystals.  Here are two examples of igneous rocks, with the difference if the rock cooled slowly or quicker or in other words, on the surface as lava or buried in the Earth as magma.

Diabase from Pinchot State Park

The last examples are of course metamorphic rocks.  The first rock is a schist, made up of abundant mica.  Mica will give the rock a sparkly shine when reflecting the Sun. This rock occupies much of the southern 33% of southern YorkCounty and is nicely exposed at Lock 12 near the NormanWoodBridge along the Susquehanna River.  Remember the term foliation.  It is shown nicely in this photograph.

Schist at Lock 12

The second example is quartzite as seen at Chickies Rock north of Columbia, LancasterCounty along the Susquehanna River.  This rock was sandstone (sedimentary) but later heat and pressure caused the sand grains to weld themselves together to make larger silica grains, which changed the texture and formed quartzite.  Quartzite is more dense than sandstone.  If you rub a piece of sandstone with your fingers, you will actually rub off sand grains from the rock.  Try doing that to quartzite, your fingers will not have any reaction to the rubbing.

Quartzite at Chickies Rock

So it is fairly easy to identify a rock.  Really, the hardest part is the first step, deciding if it is a sedimentary, igneous or metamorphic rock.  There are some great books and websites available for you to consult rock charts to give your “pet rock” a real name other than Herman.  Here are several last tips for you to remember.  Igneous rocks are usually heavy and hard to break with a hammer.  Also, igneous rock weather in a rounded shape when you see a larger exposure.  Both sandstone (sedimentary) and quartzite (metamorphic) are composed of quartz.  Both rocks will scratch a glass plate since quartz is harder than glass.  Try the rubbing test to see if any grains fall off.  Sometimes it is hard to distinguish between limestone (sedimentary) and its metamorphic equal known as marble.  Similar to quartzite and sandstone, marble contains larger crystals than limestone.  Scratch the surface of each of these rocks with a nail and then place a couple of drops of vinegar on it.  The rock should fizz since the mineral calcite is present which is calcium carbonate.  Need any other tips, email me!

For any readers who are acquainted with me know that I love to educate anyone in geology or astronomy.  Although I am probably a bit more comfortable in talking to the senior citizens (mature youth), I love to talk to all ages.  When I go on field trips with the youngsters, their minds are so open for knowledge and discovery, you can see their excitement on their faces.  One of my most memorable “kid” moments occured at the Cydonia Sand Quarry near Caledonia State Park.  One  of the youngsters during the time to explore the quarry discovered a Scolithus worm tube fossil.  The expression of her face was worth well as they say, “a thousand words.”  In fact, I have a picture of her holding your find in my collection.

This young lady found a Scolithus worm tube at Cydonia Sand quarry.

Jones Geological Services was created to host both indoor and outdoor programs to the public and groups.  I am not really sure why I became so interested in teaching folks about the earth and space, but I know after graduating from college in 1977, I returned back to York and started to conduct programs.  I was told many years ago by an friend that the best way to learn a subject was to teach it to others.  The questions you get will teach you very quickly and he was right.

A group of school students on a trip into Lancaster County.

Yes, it is the enjoyment of teaching others about one of my loves of life that is my reward.  As our programs expanded out to reach more audiences, we also had to develop new lesson plans and field trip themes.  For example, one of my favorite programs to do each year involves the Renfrew Institute in Waynesboro, Pennsylvania.  I have been conducting an indoor program and field trip for this group for over 10 years.  Each year I try to do a different program theme that will keep bringing the audience back.  Two years ago, I decided to take the group to the anthracite coal region in Schulykill County to collect petrified wood and fern fossils from a former swamp and a stop at Swatara State Park for marine fossils.  Yes, it took about 2.5 hours to drive from Waynesbnoro to Shamokin to our first stop.

This sounds like an easy trip, right?  It was the panning of this trip that tested by faith that everything would work out.  We spent 3 days in Schulykill County searching for a good fossil site to visit.  We checked road cuts and even received permission from several coal mines to search their property for fossils.  Those properties as the owners thought, did not yield any fossils for us to find, so how could 45 people find anything.  Finally, with the fieldtrip only several weeks away, a coal company’s geologist who I had spoken with a month or two prior,  called me wanting to find out if I had any luck in locating a site and permission.  I said “no” as I was driving north on Interstate 81 making one last trip into the coal region to find a site.  During that conversation, he told me about a site they owned that I could use.  After giving me directions to the site, he told me I was welcome to visit the area and see what I could find.  In my reconnaissance of the rock piles, I did find several ferns, not outstanding and not abundant, but at least it was something.

The day of the field trip arrived and as we were nearing the site, I was truthful with the 45 people onboard the bus.  I reviewed my earlier trip and I wasn’t sure how good of a site it will be based on what I found.  Well, the geology gods were on my side that day.  The folks weren’t on to the rock pile for more than 10 minutes when I started to hear people yelling in jubilation on finding fern fossils.  All I could do was to look up into the sky and say “thank you.”  In fact, there were some great ferns found there.  In fact, I took two other groups back to the same site later on.

A group of fossil collectors from Renfrew Institute

One of my favorite portions of a program is to tell folks what important geologic site, fossil, rock or mineral is found “in their backyard.”  For example, many folks are always curious about those rocks at Rocky Ridge County Park that have rounded pebbles in them.  Usually, their first reaction is that the rock was formed by a glacier.  I actually tell them that this rock is one of the oldest sedimentary rocks in Pennsylvania and the conglomerate was formed near a beach of an ancient ocean.

An outcrop of conglomerate at Rocky Ridge County Park

Usually, there is one or two students in a class that seemed to always want more information, even after the class ends.  So, I tell them about other sources that can be checked out online or I inform them of my future programs for other organizations.  Anyone wanting to learn more about what is beneath their feet will never walk away from me feeling I haven’t filled their minds with more information.   I guess it is something like mud sticking to your shoes.  The more mud that becomes stuck, the more it attracts.

Actually, through these programs I have made some great contacts to access a property that I wanted to investigate for its geology.  Or I find someone who believes they have found a fossil and wanted me to check it out.   In most cases, the fossil turns out to be something else much more unexciting that they hoped.  However, in one case, a gentleman who I am now friends with and has taken him out in the field with me, showed me a specimen he found near Emigsville.  He told me it was a trilobite and he wanted me to see it.  We met one day for me to see his specimen and I think my eyes nearly popped out of their sockets.  It was really a trilobite, not complete, but the head and body sections were clear as day.  The gentleman told me where he found it along Locust Lane.  I drove past the site and verified that the shale exposed there does belong to the most abundant fossil-bearing rock in York County known as the Kinzer Formation.  Unfortunately, I never found a fossil at the site.

A trilobite found along Locust Lane

A number of years later after doing a PowerPoint program on York County geology in which I included a picture of the trilobite, a woman approached me and said she had what she thought was a trilobite from Locust Lane.  She drove home and returned with the specimen and yes, although smaller than the first trilobite I saw from my friend, her trilobite was complete.  What a great find!!!   So I often do learn when I do programs.  It is a win-win situation.

Unfortunately, with the change of Pennsylvania’s education program, geology is not a strong subject in pre-high school grades.  If earth science or astronomy are included in their science lesson plans, the teacher often will skip over the subjects because they are not comfortable with the topics.  One of favorite school trips was the 8^th grade geology class at Elizabethtown Middle School.  That’s right, an 8^th grade geology class where they studied and did creative projects all school year.  Twice a year I would lead the class on field trips through Lancaster County, showing them concepts and rocks that they had read about in class.  My point here is that getting out and seeing the earth is the best way to learn geology.  Put your hands on it and feel it, look at it for its color and texture and let your mind wander how this rock or fossil got here.  Unfortunately, this class has been discontinued.

A student learns how to use a Bruton compass

Last spring, I talked myself into stepping out of my comfort zone.  Since 2008, I have presented geology programs to the OLLI senior citizen group held at Penn State – York campus.  Well, I had a request to do a geology of Colorado class in preparation of a trip OLLI was taking to the scenic western state in August, 2012.  I accepted the challenge and had a wonderful time teaching the 3-week course.  It was gratifying to hear from several trip goers who had my Colorado class, as they reviewed some of their favorite buttes or massive rock outcrops with me.

A group of OLLI students on a field trip

Ok, for you David Letterman fans, here comes the Top Three Rock Exposures in York County!  Whoever cared about this category anyway?  I know someone who would respond “It is only a stupid rock, who cares?”  Yes, it is only a rock, but as you find out, these exposures have played a part of our local culture and provides us some information about our past.

Number 1 on the list is Indian Rock located in York Township along the Codorus Creek at the base of Indian Rock Dam.  Um, I wonder if the name of the dam had anything to do with Indian Rock.  In that case how about the naming of Indian Rock Dam Road, Indian Rock Elementary School or Indian Rock Campground?  This outcrop wasp icked as my favorite because of its significance to the area and it carries with it one of my favorite stories in my geologic experience.   As one who has learned about the geology of York County through research and reading of historic geologic reports, a picture of an exposure on a floodplain from George Stose and Anna Jonas’s 1939 classic report on the geology of York County keep coming into my mind.  I had never found this site, although their brief description states it is a quartzitic rock outcrop was located one mile north of Brillhart Station.  According to these two geologists, this outcrop is the remnant of an anticline (arch-shaped fold).

Indian Rock looking to the east (Jonas and Stose, 1939)

Ok, so I put the outcrop on my bucket list with intensions to locate this exposure in my spare time.  I didn’t have to wait for a free moment.  A photograph of a swimming hole around the Codorus Creek with a whale-back shaped rock outcrop named “Indian Rock” in the York Dispatch’s “Around Town” column by legendary writer Harry McLaughlin, asking if anyone knew its location.  Wait a moment, I should know where such an exposure is, but I didn’t.  I got my wife, Lou Ann out of bed early the next morning and told her, we are going to solve a mystery.  We both like to solve such puzzles, particularly when it involves geology or local history.  So off we go with the only clue of the Stose and Jonas picture and the “Around Town” photograph in hand.  We stop at the Indian Rock Dam office and inquiry.  No help there.  We go to Indian Rock Campground and guess what, no help there.  Geez, doesn’t anyone look at rocks?

We stop at a private residence on Indian Rock Dam Road near the railroad tracks and after showing them the newspaper article, the owner replies “There is a rock back behind the house, but not sure if it is the one.”  Great news and with permission we walk through the woods paralleling the Codorus Creek and guess what?  This magnificent rock rose right out of the floodplain.  What a strange place for an exposure.  No other rocks in sight and we have this 60-foot long, 15-foot high piece of Earth’s crust.  We verify this is the locality both in the postcard.  After inspecting the quartzite outcrop identical to what was described by Stose and Jonas, we discovered the only way to take a picture of this locality was from the other side of the stream, back on Indian Rock Dam property.

Indian Rock as seen from the west side of the Codorus Creek

Off we go with smiles on our faces as we returned to the property where we started.  Continuing our conversation with the staff of the flood protection structure for York, we told them we found it and guess where it is, at the base of your spillway.  Granting us permission to walk down the hill to the stream, we got the picture we were seeking.  Harry McLaughlin was happy to receive the picture from us commenting “I knew you could do it.”

What makes Indian Rock so cool to geologists is the fact that this “whaleback” sticks out because all of the surrounding softer rock has been weathered and eroded away.  Quartzite is rather durable to the climate compared to the surrounding rock.  Also, Indian Rock is the core of an anticline and shows just how much the rocks in this portion of York County has been through with two crustal collisions and the rifting apart of a continent.

#2 on the list is the Accomac roadcut in Hellam Township.  For those traveling to the popular Accomac Inn for dinner, this is the roadcut you see on the right-hand of the road just before arriving to your destination.  What makes Accomac just interesting?  It is one of the few sites (and certainly the best) where you can find volcanic rocks.  One of the most common questions I receive is “Were there volcanoes in York County?”  Right here is the proof.  Exposed here is a rock known as a metabasalt.  Basalt is a volcanic rock composed of dark-colored minerals and has its origin on  the ocean bottom.  “Meta” has been added in front of “basalt” since the rock has been through several periods of heat and pressure with our geologic history.

The Accomac roadcut looking east

The rock here is a greenish color due to the presence of chlorite and small amounts of epidote.  Look carefully and you will see rounded quartz pods (some up to 12-inches across).  These were gas bubbles in the lava which eventually broke and later filled in with quartz, chlorite, epidote and a trace of copper.  That’s right, I said copper!!  Copper frequently forms in a volcanic setting such as this.  In fact, the same rock is exposed in larger amounts in South Mountain near Greenstone, Iron Springs and New Hope, Adams County.  Mineable copper deposits were worked in this area in the 1800’s into the 1920’s.

If you walk toward the west end of the roadcut, look for yellowish-green veins cutting through the metabasalt. This is antigorite, a serpentine mineral.  Nice hand specimens can be easily collected here.

Antigorite in metabasalt from Accomac

When you collect your specimen of metabasalt, remember how this rock was formed about 600 million years ago.  This was what geologists called a divergent boundary where two crustal plates were moving apart.   Today’s Mid Atlantic Ridge would be a good example of what Accomac looked like as a continent was tearing apart in the Precambrian Era.

For a bonus by stopping at Accomac, carefully cross the road and look at the beautiful waterfalls.  The water is flowing over metabasalt.  Notice the potholes and the wearing away of the rock by the stream erosion.

Potholes in the stream at Accomac

Location #3 has been talked about in this blog before but is worth talking about because of its accessibility and geology.  This is the Rossville roadcuts just north of this small town in Warrington Township.  Traveling north of Old York Road, the first roadcut on the right is diabase, an igneous rock that was magma but cooled into a rock deep beneath the surface.  Because of the slower cooling than compared to the magma on the surface (lava), the magma cooled slower forming larger crystals.  Here the rock is called coarse-grained.  You will notice several drill holes in the rock.  These were made by one or more geologists who conducted research on diabase in Pennsylvania.

My Messiah College Earth Science class interpreting the diabase outcrop

Look at the cracks in the rock or on some of the loose diabase laying at the bottom of the hill.  You might be lucky to find some white radiating crystals belonging to the mineral stilbite.  If you find small cavities in the stilbite veins, use a microscope or hand lens to try to spot small “cubic” crystals.  The minerals heulandites and chabazite are also found here.  Although not economically valuable, these are nice minerals to collect.  Water flowing through the cracks and the rock have formed this minerals.

Traveling up the road to just over the crest of hill, you cannot miss a large hole in the roadcut.  The rock here has changed from the first roadcut.  This rock was originally sedimentary in origin but when the magma intruded up through these sedimentary rocks, the heat baked them into a metamorphic rock known as a hornfel.  Various minerals form as a result of this reaction between the chemistry of the sedimentary and magma.  Garnet, epidote and actinolite are common here.  Since the construction of Old York Road in 1974, people have been collecting azurite (blue) and malachite (green) here.  These are two copper minerals are only found on the outside of the rock so there is little use to break them open.  However, using a special microscope, one could detect small  blebs  of native copper inside the rock.

Azurute and malachite at Rossville

If you go here to collect, it is recommended to take along a rake.  Because it is difficult and dangerous to work in the hole to extract the copper-bearing hornfel, smaller pieces of azurite and malachite can be found on the talus pile leading up to the hole.  Only two weeks ago, I found a colorful piece recently dug out by an earlier mineral collector.

My Continuing Education students from HACC search for copper minerals at Rossville

You want to try something different?  Travel to the copper hole after dark with a battery-powered black light.  Opal hyalite is found on the edges of some of these hornfels and under a black light it illuminates a pale green.  Opal is formed by water through and around the rock creating what is called a secondary mineral.

Finally, several years ago while I was visiting the copper hole on my way home from another project, a was approached by an older gentleman who seemed interested in why the hole was in the road cut.  After chatting with him for several minutes about the azurite and malachite, I learned I was speaking to former Pennsylvania governor,  George Leader.  He owns a farm near Rossville and was always curious about the attraction to this location.  Sometimes you just never know who you might talk to when you out and about, but it is always interesting.

One of Jones Geological Services’ biggest goals is educational programs, including field trips. One organization that has been using our talents is Renfrew Institute of Cultural History in Waynesboro, Pa.  This is probably the 10th year that we have provided the public in Waynesboro with an indoor program followed by a field trip with some sort of theme.  We discovered several years ago that the public loves to go collecting for either minerals or fossils. This is also a great way for a family to spend a day together discovering natural finds such as fossils. After doing programs for nearly 30 years, I can tell you that there is still nothing that outdoes the smile on a 10-year old child’s face after he or she found his or her first fossil.  It is one of those experiences when you say to yourself, “This type of work is really worth it.”