6O PENIKESE. 



boulders. We seldom find median moraines in 

 America. The Arctic glaciers encroach largely upon 

 the sea. Our continent has once extended into the 

 sea in the shape of a drift. The level at which the 

 drift extended over all these islands was the same. I 

 think that these islands were once mainland. Local 

 glaciers have been described in many localities, es- 

 pecially by Professor Dana; but they are the effect of 

 a great northern drift and not from local causes, as 

 might be implied." 



Toward the last of the session he returned to the 

 subject and gave us his final lecture upon this won- 

 derful subject. He says: 



"Perhaps the most important feature of glacial 

 action is found in the terminal-moraine. It contains 

 a mineralogical collection from all the region around, 

 which comes from the upper regions and falls or is 

 detached by the glaciers, and all pushed together 

 toward this terminal point of the ice. To examine 

 these moraines and trace the specimens found to 

 their real or probable bed rock is a most important 

 labor of the geologist. That glacial action was once 

 carried on to an extent much greater than could have 

 been possible had the period begun with an enlarge- 

 ment of the Arctic glacier seems evident. Thus we find 

 copper identical withLakeSuperior copper in Michigan, 

 Indiana, and Iowa, and even as far as 500 miles south 

 of its origin, having distinct marks of glacial agency 

 upon it. The rate at which glaciers moved in Amer- 

 ica is not certain. In the Alps, where the slope adds 

 to the inclination, the maximum motion per day is 

 one foot; the minimum thirty inches per year. Let 

 us assume that our glacier moved 100 feet a year, 

 and it will take fifty years for the boulder to go one 

 mile or 25,000 years for it to reach its present po- 

 sition." 



[It has often struck me as a curious fact that in es- 

 timating geological time Professor Agassiz (as well 

 as others) appears to make no account of the fact that 



