40 PALAEONTOLOGY OF NEW-YORK. 



to the westward*, but extending with great force through New-York, 

 Pennsylvania, Maryland and Virginia. 



This sandstone is charged with great numbers of peculiar fossils : 

 Brachiopoda of larger size than those of the preceding strata occur in 

 immense numbers, so that the rock is often a complete mass of these 

 shells. In some places, Gasteropoda of the Genus Platyceras occur in 

 such numbers, and in such positions, that they could .only have been 

 so placed from being drifted together by gentle currents; for these 

 shells, thin and fragile like the modern Janthina (to which family they 

 belong), are preserved in great numbers in what are termed " pockets," 

 packed together in loose sand, which, in some places in Maryland and 

 Virginia, is no more coherent than the sands of a modern sea-beach. 

 These gasteropods, moreover, assume so great a variety of form and 

 modification of parts, that it often becomes extremely difficult to dis- 

 tinguish specific differences or generic relations. 



We have at this period a profusion of individuals, represented by few 

 species of this class of animals, to which we have no parallel in any of 

 the palaeozoic groups; while the preceding and following formations 

 nearly equal this in the abundance of individuals, and present a larger 

 number of species, 



Certain brachiopods, not known till the period of the Lower Helder- 

 berg group, acquire, in the Oriskany sandstone, a development truly 

 astonishing; and two genera, at least, attain at this time their acme, 

 and in the next period gradually decline. In the Oriskany sandstone 

 we meet, for the first time, so far as would appear from our New- York 

 formations, Spirifers with bifurcating costae; a character ever afterwards 

 exhibited in some species of each succeeding period, and peculiarly 

 marked in those of the Carboniferous limestones and Coal measures. 



M. DE Vebneuil, and other European geologists, have been inclined to 

 place the dawn of the Devonian period in the horizon of the Oriskany 

 sandstone, and to regard this and the succeeding rocks as separable 



* The Oriskany Mndstone continues westward, with some slight Interruptious, to Cayuga lake ; beyoud 

 w'liicb, it has been found ouly in isolated patches. 



