144 INTRODUCTION. 
causes through a period of indefinite duration, might 
have produced even a more general diffusion, but, as an 
impenetrable veil hangs over everything that preceded 
the historical epoch, and we know of no facts which cor- 
roborate this latter suggestion, we cannot place much 
reliance upon it. We must seek then for other causes, 
to explain the general dispersion of tins and other cos- 
mopolite species. 1 
Of the origin and mode of creation of organized 
beings, we of course can know nothing, through our own 
limited faculties. The subject is beyond our comprehen- 
sion, and Divine Providence has vouchsafed to us no 
revelation concerning it. The Mosaic account of cre- 
ation informs us that after the surface of the earth was 
prepared for the support of animal life, the different 
classes of animals were created at different periods of 
time, and our own experience, drawn from observation 
of the fossil remains of former animals, which have been 
preserved in the strata of the earth's crust, fully cor- 
roborate this account. But, we are limited to these 
very general facts, and must found our views of the 
local origin, and the subsequent dispersion of species 
over the earth upon such observations as we possess, and 
such reasonings as we can base upon them. 
1 A similar course of remark might be pursued in relation to Bulimus 
lubricus, and Vilrina pellui ida, the former abundant and generally diffused 
in the country, the latter rare and found only in insulated situations, but ill 
-•very ease directly upon the route followed by hunters and fur-trappers, 
ti'Mlil tiie- earliest settlement*. 
