EEVIEVV OF THE GLACIAL PERIOD. 109 



this lacustrine area lying in Minnesota and North Dakota it forms a sheet 

 of such great extent and thickness that expcisures of the underlying older 

 rocks are very rare or wholly absent, none being known in the Minnesota 

 portion of the basin of the Red River. 



By the directions in which the bowlders have been carried from their 

 original ledges, and by the courses of the glacial stria;, it is known that 

 in the northern United States and the southern part of the Dominion of 

 Canada the ice nioAed in general from north to south. In the eastern 

 provinces and in New England its current was prevailingly southeastward, 

 and the border of the ice-sheet was pushed into the Atlantic. In the 

 region of the Grreat Lakes, and from the Laurentide highlands, James Bay, 

 and the south half of Hudson Bay westward nearly to the Rocky Moun- 

 tains, the ice-flow was mostly to the southwest and south. For examnle, 

 glacial currents moving southwestward spread upon eastern Minnesota a 

 red till, thus colored by the hematite, or anhydrous sestjuioxide of iron, 

 contained in its portion eroded from the red quartzite, sandstone, and shales 

 of Lake Superior; but in western Minnesota the ice flowed southward 

 from Lake Winnipeg to Big Stone Lake and thence southeast into northern 

 Iowa, spreading a blue till, with many limestone bowlders derived from 

 outcrops of Silurian limestone strata near Winnipeg. 



Besides the stria?, till, and transportation of bowlders, another proof 

 that the drift was formed by vast sheets of land ice is sujiplied by terminal 

 moraines, or hills, knolls, and ridges of drift heaped along the ice border. 

 These moraines are found stretching in remarkably curved and looped 

 courses across the Northern States from Nantucket and Cape Cod to North 

 Dakota. The outermost bounds the areas that were overspread b)' the 

 ice-sheet during the late part of the Glacial period, which Professor Cham- 

 berlin has 'named its East Wisconsin stage ;^ and others mark the lines 

 where the ice border paused or readvanced during its subsequent general 

 recession. 



'"Preliminary paper on the terminal moraine of the Second Glacial Epoch," by T. C. Cham- 

 berliu, in the Third Annual Report of the U. S. Geol. Survey, pp. 291-402. "Glacial phenomena of 

 North America,'' forniiiiir two chapters in J. Geikie's The Great Ice Age third edition. lSft4. pp. 

 724-775. with maps. 



