THEORY OF THE ORIGIN OF THE DRIFT. 551 



Tlieory of the Origin of the Drift. 



When the phenomena of the Drift were first observed, they were 

 supposed to indicate the agency of powerful currents, such as could be 

 produced only by the most violent and instantaneous convulsions. A 

 sudden upheaval of the ocean-bed in northern regions was supposed to 

 have precipitated the sea upon the land, as a huge wave of translation, 

 which swept from north toward the south, carrying death and ruin in 

 its course. Hence the deposit was often called Diluvium (deluge- 

 deposit). Now, however, they are universally ascribed to the agency of 

 ice acting slowly through great periods of time. Hence the name 

 Glacial epoch. 



As to the manner in which the ice acted, however, opinions have 

 been more or less divided, some attributing the phenomena to the agency 

 of land-ice — glaciers — others to that of drifting icebergs. According 

 to the one, the land during this epoch was greatly raised and covered 

 with glaciers ; according to the other, the same area was sunk several 

 thousand feet and swept by drifting icebergs, carried southward by cur- 

 rents, and dropping their load of earth and stones. The one is called 

 the glacier theory, the other the iceberg theory. 



It is probable that both these agencies were at work, either at the 

 same time or consecutively ; but the decided tendency of science is 

 toward the recognition of glaciers as the principal agent during this 

 earliest epoch of the Quaternary. The more the phenomena are 

 studied, and the more glaciers are studied, especially in polar regions, 

 the larger is the share attributed to this agency. We will not discuss 

 this question, but simply give the present condition of science on the 

 subject. 



Statement of the most Probable View. — The most probable view 

 for America, and also for other countries, is, that the Drift, or at least 

 the most characteristic phenomena of the Drift, viz., the glaciatwn, the 

 unsorted bowlder - clay , and in many cases also the great traveled 

 bowlders, are due to the action of glaciers. They are therefore a land- 

 deposit, and not a sub-aqueous deposit. For general proof of this, let 

 any one study the phenomena of living glaciers, in the Alps and else- 

 where; then let him 7 study the appearances left by the recently dead 

 glaciers of the Sierra ; and then let him study the phenomena of the 

 Drift, especially the stony clay and the underlying glaciated surfaces. 

 It will be impossible for him to come to any other conclusion than that 

 the same agent has been at work in all these. In some cases still 

 more conclusive evidence is found in the existence of distinct terminal 

 moraines. 



Objections answered. — ITany objections have been brought against 

 this view, which may be compendiously stated as follows : 1. In glacial 



