The Jurassic formation on the Atlantic coast / by O.C. Marsh.

  • Othniel Charles Marsh
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: The Jurassic formation on the Atlantic coast / by O.C. Marsh. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    6/18 page 436
    It cannot, of course, be positively asserted at present that the entire series now known as Potomac is all Jurassic, or represents the whole Jurassic. The Lias appears to be wanting, and some of the upper strata may possibly prove to belong to the Dakota. The latter formation in the West often lies apparently con- formably on the Atlantosaurus beds, and besides its many fossil plants contains fragments of bones, but these may have washed out of the Jurassic clays below. Footprints resembling those of birds have also been found. The Potomac Formation. The Maryland Potomac, as we know it to-day, is the key- stone to the arch. If this is Jurassic, as now seems certain, it is a fair conclusion that the same series of deposits, north and south, are essentially of the same age. The only region along this line of a thousand miles or more, where a systematic search for vertebrate fossils has been made, is in Maryland, and here a rich fauna has been found. Doubtless in many out- crops of this formation, animal remains may be rare or absent, as they appear to be in the Triassic below, but vertebrate life we know was abundant during the Jurassic, and characteristic remains will sooner or later come to light. Taking, then, the Potomac formation as it is developed in Maryland as an eastern representative of the Jurassic, let us see what follows. The authorities on this formation—McGee, Ward, Fontaine, Uhler, and others, agree that it extends south along the Atlantic border as far as North Carolina, holding the same relative position, and the same general characteristics. That it also extends west around the Gulf border ha6 been asserted by those most familiar with its southern development, but on this point I cannot speak from personal observation. From the Potomac River northward, however, I have made sufficient explorations alongits outcrops through Maryland, Dela- ware, and Pennsylvania, to the Delaware River, to ascertain its distinctive features, essentially the same throughout, with its geological position still maintained. In New Jersey, 1 have likewise followed its equivalent strata across the state in the great series of variegated plastic clays, to the Raritan River, and again in their exposure on Staten Island, everywhere seemingly the same series of strata and of the same age. The position is a definite one, always along the line where the Jurassic must lie, if present. Along the northern shore of Long Island, the same forma- tion extends, and at many outcrops it may be seen with its characteristic features well displayed. I have recently exam- ined these exposures at many points, and all tell the same story. At Montauk Point and on Gardiner's Island, I found apparently the same deposits, but with local variations that need not now be discussed.
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