GEOGRAPHTCAL DISTRTBTTTION. Jj^^ 



tide of population is already rolling, offer, in the great 

 extent of their table-land and in the height to Avhich they 

 rise, a vast field of research to future naturalists, -where 

 they "will be able to solve many of the most important 

 questions connected with the geographical distribution 

 of the terrestrial mollusks of our country ; and only a 

 few years will elapse before these mountains will be 

 accessible, with comparative ease, to those who may wish 

 to explore them. 



Having thus noticed the most important agents which 

 are supposed to influence the extension of these animals, 

 it may be proper to give such general results respecting 

 their actual distribution, as seem to be justified by our 

 present scanty knowledge, and to be in accordance with 

 the preceding principles. And if, as before observed, 

 but httle confidence can be placed in such general infer- 

 ences, they may nevertheless be useful by excitmg 

 further investigation, and may lead the way to more 

 certain mformation. The facts hitherto observed in re- 

 lation to species, indicate the existence of several distinct 

 zoological divisions or sections of country, of which the 

 topographical characters are in general well marked, and 

 in which, respectively, causes are seen to exist adapted, 

 according to our views, to exercise the influences we have 

 named. It is not pretended that the productions of each 

 of these, even in the limited department of the terres- 

 trial mollusks on which alone they are fomided, differ en- 

 tirely from those of the others ; but, while they are more 

 or less blended in general, there are certain species which 



