Vi PREFACE. 
tions which contain scientific treatises by a variety of hands, 
such as Transactions of Societies, Journals, Magazines and 
Encyclopedias. The several treatises of which these periodicals 
consist, as far as they relate to our subject-matter, are regi- 
stered alphabetically under the author’s name in the second 
part of the work. This vast undertaking can at present be 
only partially executed, from the difficulty before alluded to, 
of obtaining access to all the periodicals enumerated in the 
first part. So far however as the compilers have been able to 
perform this part of their project they have done it conscien- 
tiously, taking such periodicals as were within their reach, 
and faithfully extracting the titles of the memoirs which they 
contain. The titles of all detached and independent works 
are also inserted in the alphabetical series, so that under the 
name of each author will be found a complete list of all his 
writings in these departments of natural history. 
As already stated, this compilation is professedly limited to 
scientific Zoology and Geology, yet it must be admitted that 
M. Agassiz has inserted, rather too indiscriminately in my 
opinion, many titles of works which are only remotely con- 
nected with those subjects. Had I been the sole compiler 
instead of the editor of the work, I should, for the sake of 
rendering it less bulky, have excluded all merely popular and 
elementary essays, all treatises on Human and Morbid Ana- 
tomy, on Ethnography, on Domestication of Animals and the 
Veterinary Art, on pure Mineralogy and Crystallography, on 
Mining and Metallurgy, and all popular Voyages and Travels. 
Too many of such works have however crept into the Cata- 
logue, and I, as editor, did not, except occasionally, feel jus- 
tified in excluding them. To have erased a work from the 
list merely because its title appeared irrelevant to our especial 
subjects would have been highly improper, and to have con- 
sulted the original work in all doubtful cases would not only 
