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. Gebiiard 
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, 
[ Paleontology III.] b 
