218 SKETCHES OF CREATION. 



N 



Fig. 81. Sketch of Glacier Furrows and Scratches at Stony Pt., Lake Erie, Mich, 

 a, a. Deep water line, b, b, Border of the bank of earthy materials, c, c. Deep 

 parallel grooves 4^ feet apart and 25 feet long, bearing N. 60° E. d. A set of 

 grooves and scratches bearing N. 60° W. e. A natural bridge. 



A result of this wide-spread scouring arid grinding of 

 the rocks was the accumulation of vast quantities of de- 

 tritus. From this source comes a large proportion of the 

 pebbles, sand, and clay which every where underlie the 

 surface-soil, and separate it from the bed-rock — an essen- 

 tial and beneficent provision, as every one knows who has 

 observed the destructive effects of ordinary droughts upon 

 thin soils resting on a rocky basis. Another effect of the 

 great glacier was the destruction of all vegetation over the 

 areas which it invaded. From season to season, and from 

 year to year, the mighty mass marched irresistibly forward, 



