PREFACE. 



The present work was committed to my charge in the spring of 1S43 ; but 

 the wnfinished state of my Report on the Geology of the Fourth District 

 rendered it impossible to devote myself entirely to the Paheontology, during 

 the remainder of that year. From the limited time at first allotted to the 

 completion of the work, it became necessary to examine cursorily all the 

 sti'ata of the system, with a view of giving several representative species or 

 typical forms of each group. This plan was continued until the end of the 

 year 1844 ; at which time I had materials prepared for a single volume, to 

 be illustrated by about 70 plates, giving figures of fossils from all the strata 

 ii-om the Potsdam sandstone to the Coal formation. I then became satisfied 

 that such a work would afford but a very imperfect and incomplete re- 

 presentation of the extensive and rich fossiliferoxts series of New- York. In 

 consideration of this circumstance, the time originally contemplated for 

 completing this work Avas extended by the Legislature at the session of 1840 ; 

 and I commenced a re-examination of the lower strata, with a view of giving 

 a more complete representation of their organic contents. The result of these 

 subsequent investigations has more than doubled the number of species at 

 that time known to me, and has increased the plates from 40, the number 

 originally contemplated for illustrating these groups, to more than 90. 



In the present volume, I have, in many instances, given much detail in 

 regard to surface and internal structure, changes of form resulting from age, 

 nature of sediment, and other circumstances. To geologists and paleontolo- 

 gists, already acquainted with these facts, some portions of this may appear 

 unnecessary ; but it should be remembered, that of the 3000 copies printed, 

 probably 2500 will go into the hands of persons unlearned in any department 

 of natural science. The work is published expressly for the benefit of the 

 people of the State of New-York; and I have, in this diflicult subject, en- 

 deavored to point out to the apprehension of all, the differences of character, 

 I Pal.eontology. I B 



