1882.] 55 [Davis. 



with his own eyes will find the hypothesis of glacial erosion as applied to 

 the Alps and to Norway, a mischievous exaggeration (arge Uebertreibung). 

 (Mechanismus der Gebirgsbildung, 1878, I, 251-2. See also Antheil der 

 Gletscher bei Bildung der Thaler. Zurich, Vierteljschr., xx, 1875, 205- 

 207.) 



G. H. Stone describes a surface of preglacial weathering between neigh- 

 boring glaciated rocks, implying a very small erosion below the old soils. 

 (Portland Nat. Hist. Soc. Proc. 1881.) 



C. 7. The Driftless Region of Wisconsin was described by 

 Whitney in 1862 (Geol. Wise, i, 99) and has been further studied 

 by the present geological survey of that State (n, 1877, 608-611.) 

 It is a district several hundred square miles in area, enclosed on 

 all sides by drift-covered surfaces. These neighboring glaciated 

 regions have lost the more delicate pinnacles of rock which still 

 remain from preglacial times on the non-glaciated area ; but this 

 loss has not been sufficient to alter the general hill and valley 

 form to any great extent, for the stream courses on the contrasted 

 districts are closely of the same character. Within the isolated 

 region not affected by ice they retain the meandering courses 

 characteristic of stream erosion in horizontal strata, and evi- 

 dently are the product of a long preglacial land existence. The 

 occurrence of the same type of valley on the surrounding gla- 

 ciated districts shows clearly that they also retain much of their 

 preglacial form, and that the broad ice sheet was powerless to 

 destroy the general features of the country. The changes that 

 have occurred are most largely the effect of drift obstruction. 

 Moreover, the Wisconsin River twice runs on and off of the 

 driftless region, showing that there is no great change of level 

 along the drift border. But the bordering drift country extends 

 directly east to Lake Michigan, of which the trough is supposed 

 to be cut out by the ice ; how is it possible that the ice should 

 have so greatly varied in its cutting power in the same lati- 

 tude, or at essentially the same distance from its source ? Of 

 course a greater thickness of ice in Lake Michigan would have 

 made some change in its action there, but this greater thickness 

 must have resulted from a preglacial wearing down of the basin 

 and if that be granted, there is no difficulty in accounting for the 

 lake without any glacial aid except that of furnishing drift ob- 

 structions to old valleys. 



