270 PROBOSCIDIA. 
concurs, however, with the localities of its most abundant 
remains, in showing that, like the Rein-deer, the northern 
extreme of the temperate zone was its metropolis. 
Attempts have been made to account for the extinction 
of the race of northern Elephants by alterations in the 
climate of their hemisphere, or by violent geological catas- 
trophes, and the like extraneous physical causes. When we 
seek to apply the same hypothesis to explain the appa- 
rently contemporaneous extinction of the gigantic leaf- 
eating Megatheria of South America, the geological phe- 
nomena of that continent appear to negative the occurrence 
of such destructive changes. Our comparatively brief ex- 
perience of the progress and duration of species within the 
historical period, is surely insufficient to justify, in every 
case of extinction, the verdict of violent death. With re- 
gard to many of the larger Mammalia, especially those 
which have passed away from the American and Austra- 
lian continents, the absence of sufficient signs of extrinsic 
extirpating change or convulsion, makes it almost as rea- 
sonable to speculate with Brocchi,* on the possibility that 
species like individuals may have had the cause of their 
death imherent im their original constitution, independently 
of changes in the external world, and that the term of 
their existence, or the period of exhaustion of the prolific 
force, may have been ordained from the commencement of 
each species. 
* Cited by Lyell, ‘ Principles of Geology,’ (1835,) vol. iii. p. 104. 
