PREFACE. 



This volume contains the descriptions and figures of all the fossils, 

 exclusive of corals and bryozoa, at this time known to me as occurring 

 in the Lower Helderberg group and the Oriskany sandstone, together 

 with the peculiar crustacean forms of the Waterlime group, which lies 

 at the base of the Lower Helderberg rocks, and marks a very distinct 

 geological horizon over several hundred miles from east to west, while 

 it is also recognized in a southwesterly direction as far as Virginia. 



The number of species described, belonging to these rocks, is 345 ; 

 and should the number of zoophytes equal those of the Niagara and 

 Clinton groups, the fauna of the Lower Helderberg group and Oriskany 

 sandstone will yield above four hundred species within a range of a few 

 hundred miles. 



With a view to the preparation of this work, collections were com- 

 menced in the rocks of the Helderberg mountains near Albany, in 1843, 

 and continued with slight interruptions to 1857 : the results of these, 

 in one small area, are given on pages 592 - 594. The collections from 

 other localities have been less persistent, but the results of all are 

 embraced in this volume. 



The collection of fossils from these rocks, purchased of Mr. Gtebhard 

 for the State Cabinet, has furnished the greater part of the Trilobites 

 described, many of the Lamellibranchiata, and some of the Gasteropoda 

 and Brachiopoda : the finer specimens of Lepadocrinus are likewise from 

 this collection. I am indebted to Ledyard Lincklaen, Esq., for the use 

 of the very beautiful specimen of Mariacrinus nobilissimus figured on 

 Plate II ; and also to Col. E. Jewett for the use of a similar specimen, 



[ PALiKONTOLOGY III.] - B 



