Mesozoic and Cenozoic Geology and Paleontology. 27 
that the drift deposits of eastern America are not to be accounted for 
‘upon the theory of a terrestrial origin or a supposed glacial period. ° 
1. It reqnires a series of suppositions unlikely in themselves, and not 
warranted by facts. The most important of these is the coincidence of 
a wide-spread continent, and a universal covering of ice in a temperate 
latitude. In the existing state of the world, it is well known that the 
ordinary conditions required by glaciers in temperate latitudes are 
elevated chains and peaks extending above the snow-line; and that 
cases, in which, in such latitudes, glaciers extend nearly to the sea 
level, occur only where the mean temperature is reduced by cold ocean 
currents approaching to high land, as for instance, in Terra del Fuego, 
and the southern extremity of South America. But the temperate re- 
gions of North America could not be covered with a permanent mantle 
of ice under the existing conditions of solar radiation; for, even if the 
whole were elevated into a table-land, its breadth would secure a suf- 
ficient summer heat to melt away the ice, except from high mountain 
peaks. Either, then, there must have been immense mountain-chains 
which have disappeared, or there must have been some unexampled as- 
tronomical cause of refrigeration, as, for example, the earth passing 
into a colder portion of space, or the amount of solar heat being dim- 
inished. But the former supposition has no warrant from geology, and 
astronomy affords no evidence for the latter view, which, beside, would 
imply a diminution of evaporation, militating as much against the 
glacier theory as would an excess of heat. An attempt has recently 
been made by Professor Frankland to account for such a state of things, 
by the supposition of a higher temperature of the sea, along with a 
colder temperature of the land; but this inversion of the usual state of 
things is unwarranted by the doctrine of secular cooling of the earth; 
it is contradicted by the fossils of the period, which show that the seas 
were colder than at present; and ifit existed, it could not produce the 
effects required, unless a preter-natural arrest were at the same time 
laid on the winds, which spread the temperature of the sea over the 
land. The alleged facts observed in Norway, and stated to support this 
view, are evidently nothing but the results ordinarily observed in ranges 
of hills, one side of which fronts could sea-water, and the other land 
warmed in summer by the sun. 
The supposed effects of the varying eccentricity of the earth’s orbit, 
so ably expounded by Mr. Croll, are no doubt deserving of considera- 
tion in this connection; but I agree with Sir Charles Lyell in regard- 
ing them as insufficient to produce any effect so great as that refrigera- 
