VIII RIVERS AND LAKES 819 - 
back, they would be dammed up, and lakes 
would result. 
Moreover, if the formation of a mountain 
region be due to subsidence, and consequent 
crumpling, as indicated on p. 217, so that the 
strata which originally occupied the area A B 
C D are compressed into A’ B’ C’ D’, it is 
evident, as already mentioned, that while the 
line of least resistance, and, consequently, the 
principal folds might be in the direction A’ B’, 
there must also be a tendency to the forma- 
tion of similar folds at right angles, or in the 
direction A’ C’. Thus, in the case of Switzer- 
land, while the main folds run south-west by 
north-east there would also be others at right 
angles, though the’'amount of folding might. be 
much greater in the one direction than in the 
other. To this cause the bosses, for instance 
—at Martigny, the Furea, and the Ober Alp, 
— which intersect the great longitudinal val- 
ley of Switzerland, are perhaps due. 
The great American lakes also are probably 
due to differences of elevation. Round Lake 
Ontario, for instance, there is a raised beach 
which at the western end of the lake is 363 
