Davis.] 52 [May 3, 



scale this work Is indicated in the Great Lakes of the central part of the 

 country (North America), and the numerous excavations that divide the 

 northern part of the continent into a sea of islands." (Illustrations of the 

 Earth's Surface, Glaciers, 1881, 52.) 



A. Penck's latest work (Die Vergletscherung der Deutschen Alpen, 

 Leipzig, 1882), referred to twice above, has been seen only since the writing 

 of this paper. He strongly advocates the glacial origin of the Bavarian 

 marginal lakes. 



In 1821, Ven^tz wrote " How many little lakes are there in the mountains 

 which would probably have been filled with earth and stones if the glaciers 

 had not formerly cleaned them out." (Soc. Helv. Mem. i, 2°, 1833, 33.) 

 This intermediate position was revived and extended by G. de Mortillet 

 in 1859 ; he supposed that glacial action in forming lakes was limited to the 

 cleaning out of preglacial detritus from valleys or basins. This was ap- 

 plied especially to the marginal lakes of the Alps, and found much accep- 

 tance among those who could not go to the lengths demanded by Kamsay, 

 but who admitted some destructive power in glaciers. (Soc. Geol. Bull., 

 xvi, 1859, 888.) 



The action of glaciers in preserving lakes by excluding the 

 deposition of sediment during the occupation of the basin by ice 

 has in many cases been very important, but this does not imply 

 any great erosive power. 



Charpentier wrote, " As the glaciers in advancing swept off the soil down 

 to solid rock, we can easily see why our lakes have not been filled by the 

 immense quantity of blocks, gravel and sand which must have crossed 

 them, or more exactly must have passed over them, and which would not 

 have failed to fill the basins if they had been carried by water." (Annales 

 des Mines, vin, 1834, 228.) 



Agassiz placed the formation of the Swiss lakes before the disappear- 

 ance of the glaciers from the low ground, and explained their escape from 

 filling up with drift by their occupation by ice. (Etudes sur les Glaciers, 

 1840, 283, 286, 314, 318, 325.) 



This idea has since been adopted by E. Desor (Gebirgsbau der Alpen, 

 1865, 136), O. Peschel (Ueber den Ursprung der Jura-Seen, Ausland, 

 1868, 1005), and others. E. v. Mojsisovics considers the larger Alpine 

 lakes preglacial ; and holds that the " abenteuerliche Aushohlungstheorie " 

 is untenable on physical as well as geological grounds. (Bemerkungen 

 iiber den alten Gletscher des Traunthales, Wien, Geol. Reichsanst. Jahrb., 

 xvin, 1868. 310.) 



The objections to the glacial origin of the larger lakes may be 

 thus summarized. The argument from necessity may be very 

 often if not always met by denying it ; for many lakes thought 



