Amid the white daisies, blooming purple vetch, cigarette butts and Snapple bottles, a block of weathered grey limestone had come to rest next to a busy state highway.
Measuring about 3 feet by 2 feet by 18 inches, the slab had broken off from an outcropping of Ames limestone that was visible about 30 feet above the road's wide shoulder.
Thousands of tiny fossil shells dotted its flat surface. Almost all were examples of a two-shelled creature called Crurithyris, which is an extinct member of a varied group of marine animals called brachiopods. Also scattered around the block were the remains of an ancient coral called Stereostylus. The white color of those horn-shaped fossils made them stand out from the darker stone.
What I was looking at lying beside the highway was evidence of bountiful ocean life about 300 million years old. While awed by the age of what I had found, I was also aware of the traffic hurtling down the exit ramp behind me. Only a few yards from the large block of fossil-laden limestone were the flattened remains and splintered posts of a downed road sign asking that "Trucks Reduce Gear."
While the highway berm was wide and the moving vehicles were about 30 feet from where I was standing, I was wishing I had worn the orange safety vest that was hanging in my hall closet.
State geologist John A. Harper had identified the outcropping of Ames limestone as a likely place to place to spot fossils -- mineralized remains of long-dead plants and animals. During the period when the limestone was being laid down, what is now southwest Pennsylvania was part of a warm sea, and water-dwelling brachiopods and coral flourished.
The Ames limestone is 3 to 4 feet thick at the road cut. It is harder than the notoriously unstable Pittsburgh red beds, which are underneath it. As the softer shale red beds erode away, blocks of fossil-filled limestone drop to the sides of the highway.
Harper had provided clear instructions on getting to this site, and I hiked the half mile or so to the fossil site. After 10 or 15 minutes of examining rocks on the berm, I found the first of several blocks of fallen limestone.
While I brought along a hammer, safety glasses and a steel chisel, I had no need of them to free up clumps of fossils. As the slabs fell, they stayed mostly in one piece. Nevertheless, plenty of smaller pieces had broken off, and within a half hour or so I had found about a half-dozen fossil-filled samples to satisfy my collecting urge.
Hemmed in between the traffic on one side and the ominous-looking limestone overhang on the other, I didn't want to hang around. I wrapped up a few potato-sized hunks of rock in sheets of newspaper, placed them in my backpack and left.
Overzealous collectors and concerns about liability and safety have reduced the locations where amateur geologists can collect specimens, according to Albert Kollar, invertebrate paleontology collections manager for the Carnegie Museum of Natural History in Oakland.
Harper said that while professional collectors coming in with bulldozers or jackhammers have caused problems, invertebrate fossils, including the brachiopods and corals found in southwest Pennsylvania, remain very common, .
"There is no reason why amateur collectors or Boy Scouts can't have some fun finding fossils like those." he said.
Kollar recommended that those interested in learning more about geology and collecting evidence of ancient life join a local gem or mineral club.
Ironically, quarry operators and other land owners, who don't want to risk liability by allowing solo collectors onto their property, are more likely to grant permission for fossil collecting to an organized group, said fossil hunter Bill Kochanov.
Pennsylvania used to publish guides to fossil collecting, but those books and others like them are mostly out of print. While some tattered copies are available in libraries or through Internet merchants, much of the information in them is out of date.
While road cuts offer some of the best locations for finding fossil-bearing rocks, collectors and high-speed traffic don't mix.
"Stay off the Interstates and stay off the Pennsylvania Turnpike," Harper advised. Secondary roads with wide shoulders offer the best option.
Anyone seeking fossil sites on private property always should get permission from the owner before collecting, the geologists agreed.
Kollar leads geology talks organized through the Carnegie Museum, which also supports a related organization named "Patrons and lauradanae Supporters," or PAlS. It is named for an extinct sea-dwelling arthropod called lauradanae, which is related to modern scorpions, crabs and shrimp.
PAlS offers occasional fossil collecting trips with an overall emphasis on understanding local geology.
"I don't want to give the impression that you can walk along the Montour Trail or through Frick Park and just bang away with a hammer," he said.
For details on the next PAlS trip, visit www.carnegiemnh.org/ip/pals_events.htm.
Len Barcousky: firstname.lastname@example.org or 724-772-0184. First Published July 11, 2010 4:00 AM