186 



PHYSIOGRAPHY 



the sea-level rise. 3. Lavas poured out from volcanoes beneath the 

 sea would have the same effect. 4. When great ice-caps develop 

 on the land, the water locked up in the ice comes from the sea, and 



the withdrawal of this water from 

 the sea must lower its surface. 

 When the ice melts, the return of 

 the water to the sea would cause 

 its level to rise. Some other factors 

 also enter into the problem. 



From the fact that old shore- 

 lines are sometimes warped, it 

 seems clear that some of the changes 

 along coasts are due to movements 

 of the solid parts of the earth. On 

 the whole, it seems probable that 

 the sinking of portions of the solid 

 part of the earth is more common 

 than their rise, because the earth is 

 Fig igi t cooling and therefore shrinking; 



Columns of the Temple of Serapis, and shrinking means bringing the 

 near Naples. outside nearer to the center; that 



is, the lowering of the surface. 



Changes of level in the interiors of continents. Changes of 

 level are perhaps as common in the interiors of continents as along 

 coasts, but they are not so easily detected, since there is, away from 

 the coast, no level surface like the sea with which to make com- 

 parisons. There are raised beaches about many lakes, as about the 

 Great Lakes, and Great Salt Lake (Fig. 182); but raised beaches 

 about a lake may result from the lowering of the lake, either by 

 the cutting down of its outlet or by great evaporation. They do 

 not, therefore, prove a rise of the land. In many cases, the old 

 shore-lines about lakes are not level, as they must have been when 

 formed. Some parts of the old shore-line about Lake Bonneville 

 (p. 149) are 300 feet higher than other parts of the same line. An 

 old shore-line about the east end of Lake Ontario is more than 400 

 feet above the lake, while the same shore-line, traced westward, 

 passes beneath the water at the west end of the lake. Such warped 



