|A scenic waterfall in "Accomac
Gorge." The bedrock is the Catoctin Formation metabasalt.
Combined with the exposures in the stream and the roadcut just to the
south, make this one of the largest exposures of the oldest formation
within the Hellam Hills. Metarhyolite is also found in the
area. The presence of these rocks prove that volcanoes did occur
in York County approximately 700-800 million years ago. Other
areas where these volcanic rocks can be found include near the Hellam
interchange of U. S. Route 30 in the Hellam Hills and in the Pigeon
Hills near Hanover.
|Hellam Township - In "Accomac Gorge", the
stream shows an evolutionary history of potholes. Here, these
potholes are formed within the Catoctin Formation metabasalts.
|Hellam Township - The most widespread formation within the
Hellam Hills is the Chickies formation. One member, the Hellam
Conglomerate occupies some of the higher elevations. A
conglomerate is a sedimentary rock that contains rounded pebbles.
In this case, the pebbles are composed of quartz. The rock is one
of the oldest sedimentary rocks in Pennsylvania dating back 570 million
years ago. Geologists think that this rock was formed in a delta
Township - Codorus Furnace is one of five iron furnaces that once
existed in York County. This furnace located on the east side of
the Codorus Creek near the junction with the Susquehanna River has been
rebuilt and is currently owned by the Conservation Society of York
The furnace operated in the late 1700's into the mid 1800's processing
iron ore mostly removed from the Earth in the Hellam Hills of York
and Chestnut Ridge in Lancaster County.
|Hellam Township - Shull's Rock provides one of the most scenic
pictures of the Susquehanna River in York County. The rock is
composed of the Chickies Formation quartzite. Here looking north,
notice the railroad bridge in the foreground. In the distance is
Brunner's Island, a coal-generation electric plant. To the right
is the Lancaster County Solid Waste facility near Bainbridge.
Notice above the railroad bridge a line crossing the river. This
is a "riffle" in the water where the Stoneybrook diabase dike
crosses into Lancaster County. The diabase is more resistant to
weathering and erosion compared to the surrounding
rock. Please note, Shull's Rock is on private
property and trespassing will not be tolerlated.
Township - At Shull's Rock, excellent examples of Scolithus
tubes are visible. In this example, these are at the top of the
bed (looking down on the tubes). Each circle represents a
tube. These tubes are believed to have been formed by a worm
boring its way through the sand some 600 million years ago. When a
geologist finds these worm tubes like in this case, it helps the
scientist to determine which way the beds are oriented. Photo by
Mary Ann Schlegel
|Hellam Township - Chimney Rock is a classic site of the
Hellam Conglomerate, the lowest member of the Chickies formation.
The rock is over 600 million years old and contains mostly rounded
quartz pebbles. Weathering and erosion has formed these two
pinnacles over time. This rock is a great teaching tool for
structural geology classes. Stretched pebbles and lineations help to
interpret the structural geology of the Hellam Hills. On private
property, permission has to be obtained from the owners. Check out