and Orography of the Earth's Surface. 307 



tent of these, and perhaps arrive at the possibility of calcu- 

 lating the space left, as well as the space occupied. This 

 simple case is more seldom than the others. Similar con- 

 siderations may be applied to elevations of beds around a 

 profound central point, a crater or a long rent. Yet, in 

 most cases of elevation with upright standing beds, there are 

 convolutions, divisions, various inclinations, fallings in, and 

 later destructions ; besides, one period of elevation may 

 complicate itself frequently with another, and make the pro- 

 blem still more difficult to be resolved. We can only re- 

 solve these by an approximative calculation by maxima and 

 minima. One can calculate nearly the surface of a chain with 

 the value of the space of its valley, and then estimate the value 

 of the space of the hills, and on the whole as a compact mass 

 of certain geometrical form, as for instance as a triangular 

 division with two truncatures at the ends. One would con- 

 sider the whole as pushed out of the soil. One should also 

 reckon what such a chain was once, and what it probably 

 lost by subsequent destructions. In that way one sees the 

 possibility at least of arriving at an approximate result for 

 the value of subsidences produced by such elevations of 

 chains. 



Great elevations of the earth's crust have left subterra- 

 nean vacuities, and their number increases with the height 

 of chains. I do not believe that there now exists voids equal 

 to our chains ; that would destroy naturally all our calcula- 

 tions. If they do really exist, earthquakes would indicate 

 them, from the sea-water entering into such spaces. These 

 are not necessary to explain the extent of earthquakes, for 

 they are in a great measure the extent of vibrations of all 

 dense bodies. 



To enlighten the solution of the former problem in question, 

 we should put to ourselves the following question : — Is it 

 possible to determine a normal depth of the sea during dif- 

 ferent times, in certain limits ; and would it be quite impossible 

 to find out, if not the value of each individual elevation, at 

 least the general value of all elevations in each period ? This 

 question is rendered soluble by what has been already ob- 

 tained by calculations upon the solution, the refrigeration and 



D 2 



