178 



GEORGE B. RIGG 



of these species growing near the summit of the ridge the tops are 

 dead, while in some cases the whole tree is dead. These facts 

 suggest strongly that the barren condition of the southern slope 

 might be due to the strong southerly wind that prevails there in 

 winter. West of this hill is a ridge so low that both the north and 

 the south slope are very gentle and there is no sharp line of divi- 



Fig. 1 Map of San Juan Island and neighboring islands. (Drawn from 

 U. S. Coast and Geodetic Survey Chart No. 6300.) 



sion between the two slopes. Here both slopes are entirely barren 

 of trees. On the basis of the wind theory this might be explained 

 on the ground that here the wind has a clean sweep across both 

 slopes. 



In an unpublished manuscript on The Glaciation of Puget 

 Sound, Mr. J. Harlen Bretz has called attention to the fact that 



