XIV 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 illustration 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, 
where 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 will appear in a succeeding 
volume, accompanied by descriptions and figures of the principal genera of 
palzeozoic fossils. 
In conclusion, I wish to express my obligations to Mr. Joun ‘Parerson, 
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. 
