So, we drove far north into Pennsylvania, ending up some 100 miles from the New York state line. There, in a farmer’s field, we spent a few hot hours peeling layers of shale from an outcropping of the Mahantango Formation, Middle Devonian (~ 390 million years ago). Tools of choice – hammers and chisels, and putty knives.
Those many millions of years ago, this was sea bottom, and the marine denizens here were a rich array of invertebrates, including trilobites, crinoids, corals, bryozoans, pelecypods, and brachiopods. Rock was shedding off mountains to the east, a source of sediment that ultimately buried these creatures. The Holy Grail of our quest was the trilobite, but only one of us was successful and it wasn’t me.
Rather, I found myself collecting coral, a solitary kind, often called horn coral. Perhaps my finds were Streptelasma, but I don’t know. These coral are in the order Rugosa and are described as rugose coral.
Please excuse the digression but the word rugose calls out for exploration. My spellchecker doesn’t like rugose which isn’t surprising since that’s often the case when trying to sift through the language involved in identifying species. This is certainly not a word that ever came close to my own personal vocabulary. But, rugose is a wonderful adjective, nestled quite happily in the English language (as attested to by The American Heritage Dictionary of The English Language, 3rd edition, 1996). It means “wrinkled” or “ridged” as in “his rugose cheek.” Botany likes it, using it to describe surfaces that are very wrinkled, such as leaves with prominent networks of veins. The word comes from the Latin rugosus which, in turn, is from the Latin ruga meaning “wrinkle.” Earlier this week, New York Times columnist Verlyn Klinkenborg wrote an interesting column about the song of the Swainson’s thrush. He briefly described the naming of this thrush, and commented:
It’s always this way with species. You go searching for their identity and end up entangled in thickets of human knowledge and language.
His particular thicket was composed of the myriad descriptions of the bird’s song, mine in this case was the limit of my vocabulary.
To the coral.
Each of these photos is of a different specimen. The outer wall (epitheca) of these fossils is often white as in the first image above. On some specimens, two interesting markings on this outer layer are clearly evident (second image). The horizontal ridges are growth lines and the vertical ridges mark the internal rib-like structures (septa) that extend down the interior of the coral. These are the wrinkles that make these coral rugose. The corals grew up and out from the small end. Identification of genus and species depends on distinguishing among such elements as the patterns that the septa make which aren’t very clear in the specimens I found. The best view above (third photo) looks into the horn of a coral, offering some detail. But many of my finds were somewhat flattened, greatly obscuring the patterns of the septa, and suggesting that the corals’ burial may not have been gentle and gradual.
The day was memorable in a couple of ways. First, the abundance of the coral was staggering, but I, for a long while, had no clue what surrounded me. Only after the day had worn on and I had tired of splitting shale, did I wander a level expanse in the middle of the outcrop, hoping to catch some mosaic-eyed trilobite staring up at me.
Curious, I thought, a flock of birds must settle in these trees in the evening, or else why is the rocky ground so covered with their dried white droppings.
But, when I crouched to scan the ground from my knees, I saw that those small blotches of white were not avian poop at all. They were solitary corals that had weathered free from the shale. With a concerted effort, I repressed that small voice that initially warned me, “No, don’t touch it, that’s bird s**t,” and I filled my bag.
The second hallmark of this day of fossil farming was bovine. As we toiled in the sun, unseen cows mooed musically at us from the other side of a cluster of trees. “Woodwinds mooing cows,” as Joyce’s Leopold Bloom aptly characterized the instruments and their sound. These unseen cows were our Greek chorus, offering a running, and often mildly negative, commentary on our efforts to unpack this shale. Usually lowing gently during the afternoon, they could protest loudly when a hammer clanged against a particularly recalcitrant piece of shale. “No, no trilobite there,” the chorus sang.
Just a moment in time involving unseen cows and fossil coral.
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