On the Phenomena of the Glacial Epoch. 243 
America is caused by the water in the Gulf of Mexico, and 
adjacent parts of the Atlantic, flowing towards the Arctic 
j Sea. It is afterwards deflected eastwards to Europe. By 
this means it imparts to the western shores of that conti- 
nent, and more especially to the British Islands, an average 
temperature higher by many degrees than that which pre- 
vails in other countries under similar parallels of latitude. 
While the influence of these currents tends, like that of 
the aerial ones we before referred to, to equalise the tempera- 
ture of the various regions of the earth, there is this remark- 
able distinction to be observed between them, — the aerial 
currents are uniformly distributed over the colder zones, 
and their influence is generally difl'used ; the oceanic cur- 
rents are limited by the channels in which they flow, and 
are consequently local in their efi*ects. 
In like manner, as there is nothing to interrupt the course 
of the heated air, the atmospheric currents continue from 
age to age unchanged ; while those alterations of relative 
level, which geology shows us to have been both frequent 
and great, may alter the channels of the deep, and divert 
the heated water now to one place and again to another, 
so that the same locality, which under its influence exhi- 
bited the verdure of a temperate sphere, may, when that 
influence is removed, be subjected to the rigours of perpetual 
snow. 
These conclusions so naturally flow from the acknowledged 
principles of mechanical philosophy, that we presume there 
are few who will hesitate to accept of them as correct. 
In examining the difl'erent hypotheses that have been ad- 
vanced on the subject, we find that which is described by 
Sir C, Lyell, in his " Principles of Geology," and originally 
brought forward iu 1833, more especially entitled to our 
consideration. Some," he says, " have been induced to in- 
fer that there never has been any interruption to the agency 
of the same uniform laws of change. The same assemblage 
of general causes, they conceive, may have been sufficient to 
produce, by their various combinations, the endless diversity 
of eff'ects of which the shell of the earth has preserved the 
memorials ; and, consistently with these principles, the re- 
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