DESCRIPTIONS OF THE FORMATIONS. 45 



20i Quaternary. In no part of the United States are the phenomena of 

 the drift displayed on a grander scale than in the Lake Superior region and on the 

 northern borders of Wisconsin. These drift materials consist of vast accumulations 

 of sand, pebbles and boulders, belonging invariably to rocks lying north or north- 

 west of their present position, with beds of clay of great thickness, evidently 

 brought from a great distance from the north by causes quite different from any 

 now in operation, and which nearly all geologists now believe to have been 

 glaciers. This material is spread over the whole breadth of the North American con- 

 tinent, down to 38 or 40 of latitude, with long tails projecting farther south along 

 the valleys, and it is also spread in the same way over the northern part of Europe. 



Minnesota and Dakota are very deeply buried in drift. At the south side of 

 Lake Superior the drift is frequently 200 to 300 feet deep, and at the west end 

 of that lake, from 300 to 600 feet thick, and it is 220 feet deep at Fargo, 

 Minnesota. The whole of the lower peninsula of Michigan is covered from 

 200 to 300 feet deep. To the southward the drift diminishes, and it becomes 

 more evenly spread over the country. It is a singular fact that in the Galena 

 lead region, at the corner of Illinois, Iowa and Wisconsin, bounded by the 

 Mississippi, Wisconsin and Rock Rivers, and in a considerable extent of territory 

 north of it, no trace of transported drift material can be found. The drif tless 

 region is 12,000 square miles in Wisconsin alone, or one-fourth the area of the 

 state. Prof. N. H. Winchell explains its removal by the action of glacial rivers ; 

 but Professors Chamberlin and Irving produce much evidence to show that this 

 district never was covered with drift, the glacier terminating northeast of it in the 

 moraine called the Kettle Range, so named from the great number of kettle-shaped 

 depressions it contains on its surface. No other state has so complete a series of 

 these deposits as Ohio, although not in so heavy a body as at places farther north, 

 and it has been well studied and described by Dr. Newberry. He has classified 

 the drift deposits as follows, in the ascending order : 1 The Erie clay, a blue or 

 gray unstratified boulder clay, so conspicuous in the North-west, and in which the 

 tunnels at Chicago are dug. 2 The forest-bed, consisting of a bed of soil, with 

 timber, the remains of an ancient forest, found in Ohio, Indiana, etc., at various 

 depths from the present surface. 3 Lacustrine deposits, stratified sands and 

 clays in Northern Ohio ; yellow clay, abounding with gravel, in Southern Ohio. 

 The Loess or Bluff formation of the West, Dr. Newberry thinks is simply the silt 

 brought down by the Missouri River, and deposited in a lake or great inland sea. 



Nearly every recently uncovered ledge of rock iu the drift-covered region has 

 its surface marked with the characteristic striae and furrows. These scratched, 

 polished and grooved surfaces prove the former existence, according to Agassiz's 

 theory, of an ice sheet, many thousand feet in thickness, moving across the 

 continent over open level plains, as well as along enclosed valleys. When softer 

 and harder rocks alternate, they are planed off to one outline or level, as if a 

 rigid rasp had moved over the land levelling all before it. On the contrary, on 

 any surface where water flows we find the softer materials have yielded first and 

 been worn out, while hard rocks will be left standing out, and show greater 

 resistance. Glacial surfaces are highly polished, and are marked with scratches, 

 grooves and deeper furrows. Sometimes the smooth surfaces are like polished 

 marble, showing that the grinding material was held steadily down in firm, 

 permanent contact with the rocky surface against which it moved, as is the case 

 with the glacier. There are many deep ancient channels filled by the drift. 



