Page:The Habitat of the Eurypterida.djvu/102

 desired to show that the eurypterids from the earliest times lived in terrestrial waters, for the Belt terrane has been shown by Barrell from purely lithological evidence to be non-marine. From the presence of mud-cracks and other structural characters of the formation he concludes that the terrane gives evidence of "two sedimentary cycles, each of which contains a strongly marked formation of mudcracked red shales, the shales alternating with sandy strata, and both judged to have been deposited on the flood plains of rivers, whose deltas had gained over the subsidence, finally filling up and displacing the shallow epicontinental sea" (14, 319, 320).

The Normanskill sandstones and shales of Catskill and the Schenectady bluestones of Schenectady, New York, are so similar lithologically and faunally that they may be considered together. Comparatively little is known concerning the details of distribution of these formations and their physical changes from place to place, yet the descriptions available and the studies I have been able to make in the field, make clear what must be the origin of the sediments. In reference to the Normanskill beds Clarke and Ruedemann make the following statement:

"The lithologic and faunal conditions at the Broom street quarry exposure were found to be a singularly complete duplication of those of the eurypterid-bearing exposures in the bluestone quarries at Schenectady. The Broom street quarry is also a bluestone quarry, the rock being mostly used in the crusher. The courses of 'bluestone' (here an impure argillaceous sandstone) are very compact, from 3 to 30 feet thick between the intercalations of black shales. There is distinct evidence of shallow water conditions, one bed being conglomeratic and largely composed of pebbles, many of which appear to be mud pebbles; another beautifully exhibiting very regular, widely separated wave marks with winnows of comminuted seaweeds and eurypterids in the troughs.

"Quite as in the bluestone quarries of the Schenectady beds, the surfaces of some of the sandstones are densely covered with rather poorly preserved seaweeds and eurypterids. It was therefore natural to expect that here too the black intercalated shales would contain better material of these fossils and possibly also graptolites that would indicate the age of the beds. They have indeed afforded a layer with