8 INTRODUCTION 



described. The calcareous matter in the shales consists almost entirely 

 of fossils and fragments of fossils, principally branches of corals and 

 bryozoa, segments of crinoid columns, and broken crinoid plates. The 

 brachiopoda are all calcareous and the original shell structure is more or 

 less preserved, depending upon the absence or presence of pyrite. 



The occurrence in such great numbers of immature shells in these 

 deposits may be explained by the luxuriant fauna which flourished in this 

 Niagara basin, by the quiet seas of this region and by the rapid sedimenta- 

 tion of the shales. The richness of the material is shown by the great 

 profusion of specimens representing the sponges, corals, crinoids, bryozoa, 

 brachiopods, gastropods, annelids and crustaceans, comprising altogether 

 about one hundred and fifty species. The lamellibranchs and cephalopods 

 were also doubtless abundant, but the conditions existing for the preserva- 

 tion of their remains were not favorable, probably on account of the com- 

 position of their shells, and but sixteen species have been noted. That the 

 fauna was protected from excessive storms and the action of sea currents, is 

 evinced by the usual perfection of the fossils. Some of the crinoids are 

 unbroken and remain attached by their roots, retaining their arms in place ; 

 also, large colonies of delicate branching corals and bryozoa still preserve 

 their unity. The specimens were rapidly buried in the soft calcareous mud 

 and show none of the eroding or disintegrating action of the water, such as 

 would have been produced had they lain for any considerable period 

 unprotected on the sea bottom. It is true that many specimens are 

 incrusted with bryozoa, annelids, cranias and other fixed and incrusting 

 forms, but the majority of these seem to have flourished during the life 

 of their hosts. 



Besides the embryonic brachiopoda occurring in these shales, there are 

 other classes represented by immature forms, notably the gastropoda and 

 crinoidea. These, with the brachiopoda, embrace almost all the young 

 forms found. The small gastropods are of little interest, on account of the 



