64 THE ICE AGE IN NORTH AMERICA. 



twenty feet above their roots. This has been done by some 

 force that has battered them from the upper side at the point 

 of fracture. Evidently cakes of ice brought down by the 

 streams indicated in the map, when flowing at various high- 

 er levels thau now, have accomplished this result ; for the 

 trunks in the main stream were battered on the north side, 

 while those in the gully worn by the lateral stream were bat- 

 tered from the west side. 



From this description the explanation would seem to be 

 evident. At some period, when the ice occupied only the 

 upper part of the valley to the north of this point, forests 

 grew over all the space lying southwest of the present ice- 

 front. As the ice advanced to near its present position, the 

 streams carrying off the surplus water from the western half 

 of the advancing glacier were suddenly turned into the pro- 

 tected space occupied by this forest, where they deposited 

 their loads of sand and gravel. A cause very likely com- 

 bining to facilitate deposition in this spot has not yet been 

 spoken of, but is evident from a glance at the maps. A trans- 

 verse valley passes just below this point from Muir Inlet to 

 the western inlet into which Glacier Bay divides. This 

 transverse valley is at present occupied by a decaying glacier 

 opening into both inlets, and sending a subglacial stream 

 through a long, narrow series of moraines, into Muir Inlet 

 about two miles to the south. Now, when a general advance 

 of the ice was in progress, this transverse glacier probably 

 pushed itself down into the inlet across the path of the ice 

 moving from the north, and so formed an obstruction to the 

 water running from the southwest corner of the main glacier, 

 thus favoring the rapid deposition which so evidently took 

 place. When this inclosed place was filled up, and the ad- 

 vancing ice had risen above and surmounted the projecting 

 shoulder of the mountain just to the north, that rocky barrier 

 protected a portion of the forest from the force of the ice- 

 movement, causing the ice to move some distance over the 

 top of the superincumbent gravel before exerting its full 

 downward force. Thus sealed up on the lee side of this pro- 



