258 OBSERVATIONS ON SUPPOSED GLACIAL DRIFT. 



the Northern United States, and especially in Northern Wisconsin, 

 we shall be the more astonished to learn that throughout nearly tha 

 wliole Lead-region, and over a considerable extent of territory to 

 the nortli of it, no trace of transported materials, boulders, or driffc 

 can be found ; and what is more curious, to the east, south, and 

 west, the limit of the productive Lead-region is almost exactly the 

 limit of the area thus marked by the absence of Drift." 



The conclusions to which Mr. Whitney has been led by the study 

 of this drifdess region are briefly as follow : — 



1. That since the Upper Silurian period this portion of Wisconsia 

 lias not been submerged, and that its surface has, consequently, 

 never been covered by Drift. 



2. That the denudaiion it has undergone has been effected by the 

 simple agency of rain and frost. 



3. That a large portion of the superficial detritus of the West 

 must have had its origin in the subaerial destruction of the rocks, 

 the soluble portion of them having been gradually removed by the 

 percolating water. 



4. The entire absence of terraces indicates that the region in. 

 question has not been submerged in recent times. No organic 

 remains other than those belonging to palaeozoic times, except those 

 of land animals and plants, have been found in the Lead-region. 



On the railway between Milwaukie (Lake Michigan) and Prairie 

 du Chien on the Mississippi, there is no point which rises higher 

 than 950 feet above the sea-level ; and the towns of Galena, Meno- 

 monee, and Dunlieth, in the Lead-region, are below the level of Lake 

 Michigan. 



§ 4. Beaches and Terraces. 



In connexion with this driftless area, the beaches and terraces 

 which form so distinguishing a feature in North America acquire 

 particular interest; 



Confining myself to those terraces which have come under my 

 own observation, I shall notice first the vast bank of sand, 55 miles 

 west of Lake Superior, commonly called the GTreat Dog Portage.* 

 The altitude of the summit of this terrace is 835 feet above Lake 

 Superior, more than 800 feet above Lake Michigan, and 1435 feet 

 above the sea. 



• For a description of the Great Dog Portajre, see * Narrative of Canadian Exploring Expe* 

 ditions cf 1857 and 1858.' Also Reports on the Nortli-west Territory, 1859. By the Author. 



