Mesozoic and Ccenozoic Geology and Palaeontology. 215 



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 requires 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 if it 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 Norwaj^, and stated to support this 

 view, are evidently nothing but the results ordinarily observed in ranges 

 of hills, one side of which fronts cold sea-water, and the other land 

 warmed in summer by the sun. 



The supposed effects of the varying eccentricit}" of the earth's orbit, 

 so ably expounded by Mr. Croll, are no doubt deserving of considez-a- 

 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- 



