BI6SBY PALJSOZOIC ROCKS OF NEW YOBK. 279 



lower organisms (the former consuming the latter as food), was a 

 governing and universal law. The earhest animals are the Bra- 

 chiojyoda, Annelida, and Trilobites, in distant localities, usually of 

 the same genus, seldom of the same species. They exercised their 

 instincts on rocky or on muddy bottoms, and amid tangled masses of 

 sea-weed. In this last position we may find infinite numbers of 

 minute Trilobites (Forchhammer), an order of high rank in the great 

 series of Invertebrate development. The existence of a compound 

 eye in the Trilobites of the Potsdam Sandstone (Upper Mississipi, D. 

 D. Owen) is a striking circumstance. 



Of the exact nature of all these operations, we shaU probably 

 never obtain more than a general idea, although framed on the 

 principles ruhng at the present day, because elements, vital and 

 physical, existed, of the kind and amount of which we are entirely 

 ignorant. Thus, not to speak of coast-lines and other oceanic con- 

 ditions, the Tunicata might have been numerous and influential, as 

 well as the Rhizopodous tribe lately discovered in great abundance 

 by Ehrenberg in the very earliest Silurian strata near St. Peters- 

 burg. Some parts of the animal kingdom may have been lost for 

 want of a speedy removal within the embrace of a preserving ma- 

 terial, from the many destructive agencies which labour unremit- 

 tingly in all parts of the ocean, the simplest structures disappear- 

 ing soonest. A glance at the General Table of the Silurian Fos- 

 sils of New York, will at once convey more information as to the 

 animals composing these usually internecine societies than could be 

 spread over many pages. I shall now select a few leading parti- 

 culars regarding the successive appearance of the Silurian fossils of 

 ]^ew York, reviewing generally the newly placed fossils as they 

 originate in the series of strata. 



We may here remark that nearly all the genera of New York 

 Siluria were introduced in its middle and lower stages, a diminu- 

 tion of creative energy having prevailed in the upper stage. The 

 Devonian of New York is marked by a plentiful and interesting de- 

 veiopment of new forms. 



1. Potsdam Sandstone, — Plants or plant-like fossils make their ap- 

 pearance first. In Wales but few have been collected and described. 

 In New York, however, they are apparently much more numerous, 

 and occupy nearly every arenaceous group upwards into the Clinton 

 Sandy beds, where they culminate. Up to the present day, the 

 fucoid markings have not been sufficiently studied, although full 

 of important information. They are all marine, and occur chiefly 

 in the sandstones which fringed the ancient coasts. The very in- 

 teresting Brachiopod, the Lingula, appears in Potsdam sandstone; and 

 in certain spots individuals are multitudinous. Abounding most, 

 like many others of their order, in Trenton Limestone, they are found 

 in Utica Slate and the Hudson- lliver rocks, and are then absent 

 upwards through many epochal centres, to reappear in Devonian 

 strata. This seems to be a law ; for the same takes place in Wales 

 and other countries. Co-tenants with the Lmgulce are two genera of 

 Tiilobites — one lately discovered in the north part of the State of 



