466 



SCIENCE 



[N. S. Vol. XXXIII. No. 847 



Evidences of Pleistocene Crustal Movements in 



the Mississippi Valley: J. tj. Todd. Read by 



abstract. 



Eeeent studies show that the glacial deposits of 

 Kansas indicate: (1) A marked easterly trend. 

 This appears from the direction of striffi, charac- 

 ter of bowlders, etc. The ice came from the Min- 

 nesota valley, not from the Dakota. (2) The 

 edge of the ice reached, in Pottawattamie County, 

 Kansas, an altitude of 1,500 feet A. T. Taking a 

 common point in northern Kossuth County, Iowa, 

 and assuming a uniform average slope, it is shown 

 that with the surface at present altitudes, if the 

 ice reached Blaine, Kan., in the Kansan epoch, it 

 should have reached scores of miles farther east 

 in northeastern Iowa, and seventy or eighty miles 

 further southeast in central Illinois, than any 

 trace has yet been found. Prom this it is argued 

 that the surface at that time was higher in the 

 latter localities and lower in Kansas. 



Corroborating facts are found: (1) in the 

 trough of the Mississippi being 100 to 200 feet 

 deeper than is now necessary to fit the present 

 levels of drainage, while (2) in Kansas the levels 

 of pre-glacial drainage and Kansan drainage 

 were 80 to 100 feet higher than at present. (3) 

 The stronger easterly trend in eastern Iowa of the 

 ice of the lowan epoch, as compared with that of 

 the Kansan agrees with the conclusion that the 

 change of levels took place between the two 

 epochs, presumably in response to the presence 

 and weight of the ice. 

 Fault Scarps of the Basin Ranges: Chas. E. 



Keyes. Eead by abstract. 



In the instance of the Basin-Eange type of 

 mountain structure normal faulting on a pro- 

 digious scale was long regarded as the principal 

 factor. Its mountain-block was considered as up- 

 raised. The face of the hard mountain rook rising 

 abruptly out of the less resistant valley deposits 

 was believed to represent a true fault-scarp. This 

 hypothesis is not exclusive; nor is it very satis 

 factory. 



A main objection to the theory is the fact that 

 the evidences of recent displacement are seldom 

 ever disclosed at or even near the so-called fault- 

 scarps. Whenever the line of major faulting is 

 discovered it is miles away from the mountain 

 foot — out on the intermont plain. 



On the theory of general denudation of arid 

 regions chiefly through means of eolic rather than 

 aqueous agencies the belt of maximum deflation 

 is at the foot of the desert ranges — ^where the 



mountain meets the plain. Within the limits of 

 this narrow belt the topographic result is a tend- 

 ency towards a steep, plain-like slope. This pied- 

 mont belt chances also to be the horizon where 

 torrential water action is most pronounced, cut- 

 ting deep canyons in the mountain and spreading 

 out detrital fans on the plains. In the struggle 

 between water and wind for corrosive supremacy 

 the results in the mountain area are a succession 

 01 sharp ridges trending at right angles to the 

 range-axis, sharply truncated at their lower end 

 by deflative action. The faceted mountain foot 

 thus produced resembles closely the ideal effects 

 of a fault-bounded upraised mountain-block the 

 dissection of which is well advanced. 

 Modified Drift in Minnesota: Wakeen Upham. 



In respect to their origin and mode of deposi- 

 tion the drift formations of the Ice Age comprise 

 two classes: (1) glacial drift, in the various 

 phases of the till and morainic deposits, produced 

 directly by the agency of ice-sheets, without modi- 

 fication by water; (2) modified drift, derived 

 from erosion and transportation by land ice, but 

 also to some extent transported and deposited by 

 water, being thus waterworn, assorted and more 

 or less stratified. 



This second class of the drift deposits, described 

 in its development in Minnesota, includes the val- 

 ley drift gravel, sand and clay, and also frequent 

 tracts of sand and gravel plains outside the pres- 

 ent courses of drainage, but occupying areas where 

 considerable streams of water, well laden with 

 sediments, were discharged from the melting and 

 retreating ice fields. Eelatively small parts of the 

 modified drift are amassed here as kames and 

 eskers, which are respectively knolls and long 

 ridges of gravel and sand formed by the brooks 

 and rivers of the glacial melting, the heaped and 

 ridged form of these deposits being due to accu- 

 mulation at the mouths and in the ice-walled chan- 

 nels of the streams. 



The ratio or proportion of the modified drift 

 and glacial drift in Minnesota is estimated as one 

 to three or four. This somewhat large proportion 

 modified and deposited by water, is regarded by 

 the author as an evidence that much of the drift 

 was contained in the lower part of the ice sheet, 

 and that it was finally exposed on the surface of 

 the waning ice fields to the action of streams 

 formed by the melting and by attendant rains. 

 Fluctuations of the Keewatin and Lairadorean 



Ice Currents in the Vicinity of Minneapolis and 



St. Paul: Wakren Upham. 



The currents of glaeiation in western and south- 



