BLANCH AED OR DEFIANCE MORAINE. 607 



to reach to the divide, the size of the lakes varying with the position of the 

 ice margin. 



The greater altitude of the silts at the southern end of the Cuyahoga 

 Valley than at the northern presents an interesting problem. The silt may 

 have reached, at one time, as great altitudes along the sides of the northern 

 portion of the valley as it presents on the southern, and have been removed 

 afterward by the advancing ice sheet or concealed by its morainic deposits ; 

 or it may never have had as great altitude in the northern as in the south- 

 ern portion of the district, the northern portion being a deep-water and the 

 southern a shallow-water deposit. Since it is a partially concealed deposit 

 its limitations, both geographic and hypsographic, are difficult to determine. 



The extreme rarity of jDebbles seems difficult to explain, for if the silt 

 were deposited in narrow lakes outside the ice sheet it is to be expected 

 that tributaries would discharge large amounts of coarse material with the 

 fine into the valleys occupied by these lakes, which would make a percep- 

 tible increment to their deposits. This coarse material might, however, 

 have been dropped at the borders and only the fine material have passed 

 out into the midst of the lake. A more careful examination of the gorges 

 tributary to the valleys may throw light upon this matter. 



The striae of this district, so far as observed by the writer or reported 

 by previous observers, are represented on the glacial maps (Pis. II, XI, 

 XIII, and XV), and their bearings are given in the table of striae below. 

 In general, the striae bear directly toward the moraines; thus, in the vicinity 

 of the lower course of the Cuyahoga, they bear southeastward; in the 

 Sandusky-Scioto Basin, southward; in the Maumee Basin, west of the San- 

 dusky River, south westward to westward, while in southeastern Michigan 

 the bearing- is north of west. There are, however, slight changes of course 

 in the ice currents, shown by cross striation or by lack of harmony in the 

 bearing of striae in neighljoring districts, which may be better comprehended 

 by reference to the maps than by a description. 



The greatest variation on any single surface which the writer has 

 noted is that east of Vermilion River, near the line of Erie and Huron 

 counties, where the striae appear at nearly all angles, from S. 19° W. to 

 S.. 77° W., their prevailing bearing being S. 35° W. They all consist of 



