PREFACE. 
XIII 
specimens not in my own or the State collection. To several other persons 
my obligations are also due in particular instances, which are cited in the 
body of the work. 
Dr. T. R. Beck, with his characteristic liberality in matters of science, has 
allowed me free access to the collection of the Albany Institute, which 
contains many valuable and unique specimens. I have cited, under the 
descriptions, several specimens figured from this collection, and I shall be 
farmer indebted to the same for materials for the next volume. 
To my friends out of the State, who have furnished me with specimens 
from the same formations, for comparison with those of New-York, my 
especial thanks are due. Among these I may mention Messrs. Joseph Clarke, 
J. G. Anthony and S. Carly of Cincinnati, and the Rev. Mr. Christie of 
Oxford, Ohio, who have liberally forwarded to me many valuable specimens, 
by the aid of which, in many instances, I have rendered my descriptions 
and illustrations more complete than I could otherwise have done with the 
specimens from New-York alone. 
Among the species described and figured, are a few which have not yet 
been obtained in the State of New-York, but which may hereafter be re¬ 
cognized, as more careful investigations are made in the same strata. These 
species are so intimately associated with others which are well known and 
abundant in this State, that I considered it desirable to represent them in 
their true place. 
Since this volume has been printed, the Legislature of 1847 have, with 
munificent liberality, passed a law for the completion of the work, and have 
authorised 250 plates to be engraved. This number, judging from what I 
already know of the succeeding strata, will be sufficient for ample illustration 
of the entire series. 
The succeeding volume will contain the descriptions and illustrations of 
the fossils of the strata, from the Hudson-river group, up to the Oriskany 
sandstone inclusive, and will appear in the course of the ensuing year. The 
remainder will follow as rapidly as may be consistent with accuracy in the 
determination of their specific characters and geological relations. In the 
mean time I shall embrace e very opportunity of adding to the present portion 
of the work, by arranging materials as they may come to hand for sup¬ 
plementary plates. I shall therefore feel under great obligations to any friend 
