PREFACE. 



who may have it in his power to furnish me with species from the lower 

 rocks, not here described, or who can aid me in obtaining specimens for the 

 better ilkistration of those species but imperfectly represented in the present 

 plates. 



Many of the difficulties attending the preparation of this work thus far, 

 are entirely or partially removed ; and I confidently anticipate being enabled 

 to bring forward the succeeding parts of it more rapidly, and, so far as 

 regards the artistical part, in a manner more satisfactory to myself and the 

 public. The succeeding strata are better known, and more extensive col- 

 lections have been made from them ; and there are also more numerous 

 localities, and better exposures of the strata. I shall also be able to avail 

 myself of the results of previous labors in the Fourth Geological District, 

 Avhere I have already carefully studied the strata and their contained fossils. 



The increased number of species from the lower strata, resulting from my 

 investigations since 1844, and the consequent expansion of the volume, has 

 compelled me to omit the plates already prepared for illustrating the suc- 

 ceeding strata, which were engraved in 1843 and 1844. From the same cause, 

 the sketch of the geology of the State, which I had proposed to precede the 

 descriptions of the fossils, has been deferred, and Avill appear in a succeeding 

 volume, accompanied by descriptions and figures of the principal genera of 

 palaeozoic fossils. 



In conclusion, I wish to express my obligations to Mr. John Paterson, 

 who has had the entire direction of the typographical arrangement of the 

 volume, as well as the correction and revision of the proofsheets. I have 

 also been indebted to his literary and scientific knowledge, for the general 

 accuracy of the work. 



