PREFACE TO THE SECOND VOLUME. 
This volume contains descriptions and figures of all the fossils yet observed 
by me, whether collected by myself or others, in the Medina sandstone, 
Clinton group, Niagara group, Coralline limestone and Onondaga-salt 
group ; the entire number of species being 344. As announced in the first 
volume, I intended to include in this volume the descriptions and illustra¬ 
tions of the fossils of the Lower Helderberg ; but it soon became apparent 
that the number of plates would be too much increased, and it was there¬ 
fore necessary to terminate the volume with the Onondaga-salt group. 
The numbering of the plates in this volume extends to 85 ; while the 
actual number, from intercalation, amounts to 101. 
The engraving for this volume was commenced in 1847; and during 
the year 1848, nearly all the plates were given in hand to the engravers. 
In February, 1849, there remained to be given out the drawings of plates 
35, 36, 37, 38, 60, 70 and 73 a; and the printing of the volume was then 
in progress. After having proceeded as far as the 120th page, and finding 
that the engraving was likely to be much delayed, I suspended the further 
printing at that time, for the purpose of making a re-examination of the 
corals and bryozoa, which resulted in the ascertaining of nearly as many 
additional species as possessed before. These additions to this class of fos¬ 
sils have increased the number of plates between 34 and 41, by an amount 
equal to those indicated by letters. 
With the exception of the last fifteen pages, the printing of this volume 
was completed in the early part of 1850 ; but the engraving has not been 
finished to permit its appearance till 1852. In the mean time several works 
have appeared, in which species, identical or allied with those here de¬ 
scribed, have been published. To those authors, therefore, whose publica¬ 
tions bear date anterior to this volume, but which are not referred to, this 
