266 THE ICE AGE IN NORTH AMERICA. 



lee side of a prominence in which a north-and-south glaci- 

 ated surface conld be protected from the force of the eastern 

 current, we find that it was protected, and the glaciated sur- 

 face is as fresh on the removal of the soil as it is anywhere. 

 In places the beveled edges 'of earlier grooves are perfectly 

 distinct where the second cross-movement has obliterated a 

 part of a groove, and left still untouched the portion of the 

 earlier groove which was protected by a ridge. Within a 

 half mile of each other there are grooves several inches in 

 depth running at right angles to each other. For instance, 

 upon the west side of Gibraltar (which is a small, rocky island 

 at the mouth of Put-in Bay, close to South Bass Island), there 

 are deep grooves, running north by south, made by the sec- 

 ond movement; but they were perfectly protected by the 

 rock, which received the brunt of the third movement as it 

 came from the east. One half mile west, and a little south 

 of this point on the main island, where there is a shallow 

 valley across the island, the east-and-west grooves are equally 

 striking. This was doubtless the movement whose record is 

 left in the moraine of the Maumee Valley, as already described 

 by Gilbert * 



4. There were also indications of still a fourth movement, 

 which set in when the ice had receded so far that the obstruc- 

 tion presented by the elevation of the water-shed to the south 

 would no longer compel a westerly movement. But, when 

 the ice-front was between these islands and the south shore, 

 the movement would again be, according to theory, to the 

 south, at right angles to the first and third movements. This 

 last movement, however, was probably feeble and not of long 

 continuance. Still, there are some signs of it in the shape 

 of shallow striae across the second set of east-and-west fur- 

 rows. While all this is witness to the efficiency of ice as an 

 eroding agency, it conveys the impression that the erosion 

 accomplished by each successive movement was concentrated 

 in special channels, and was nowhere excessive. 



* See p. 207 



