■PREFACE, 
XI 
identify some additional ones from Mr. Conrad’s notes, and from labelled 
specimens in the State Collection. 
In describing the species, I have preferred to follow the stratigraphical 
order, beginning with the lowest rock ; considering the geological succession 
of species to he more in accordance with the design of this work, than a 
zoological classification. I have nevertheless endeavored, under each rock, 
to arrange the fossils according to their zoological affinities, beginning with 
the corals, which are preceded by the marine plants where any are known 
in the rock. This arrangement has not been so perfect as could have been 
desired; but the future volumes will be so planned, by a double series of 
numbers for the pages, as to admit of being separated, and a complete 
zoological arrangement of the species made. What we most need, however, 
for the purpose of facilitating geological research, is a true representation of 
the species in their order of succession, arranging always those from separate 
rocks or groups by themselves. In this manner only can they have their true 
value affixed to them, and their relative chronological importance assigned. 
The increased number of species over those before known as belonging to 
these strata, the larger part of which appeared to be new, has made me 
diffident in advancing the results of my researches, and in claiming, not only 
a large number of new species, but also a considerable number of generic 
forms not before recognized. Since the descriptions of species contained in 
this volume were prepared, and while the early pages were passing through 
the press, I have had the rare opportunity of several times consulting M. de 
Verneuil in reference to this part of the subject. His examinations have led 
to the same result, and he has encouraged me to publish my species as they 
now stand, assuring me that the greater part are new, and quite distinct 
from the published European forms. Subsequently I have had the pleasure 
of submitting some of my specimens, and the results of my examinations, 
to the learned M. Agassiz, who has honored me by expressing a favorable 
opinion of my labors. Although, encouraged by such friendly expressions on 
the part of able naturalists, I have less anxiety than I should otherwise have 
felt in the publication of the volume, I am nevertheless fully aware that 
there is much room for improvement. 
Of my scientific friends, and of the scientific public generally, I must ask 
indulgence, while they consider the circumstances under which the work 
