306 M. Ami Boue on the Palceohydrography 



In this way we should obtain an idea of the true site of 

 volcanic action ; or of the very unequal limits where there is 

 in the earthy mass already complete rigidity on one side and 

 igneous fluidity on the other. If, according to this, the depth 

 of volcanic action is pretty great, still it is not so, as some 

 people would conclude, from the extent of the vibrations of 

 earthquakes. As that depth must be in extensive relation 

 with our highest chains, and as the height of our highest hills 

 even surpasses the value of their parts in the earth which 

 lie below the sea-level, it is not at all certain that this may 

 be everywhere the case. On the contrary, the wrinkles 

 and low parts of the earth's surface, and the depth of the 

 volcanic action, or the fluid focus, must have various values 

 according to the different places of the earth. This also 

 clears up the different scales of temperature which have been 

 established for different places by the observations on the 

 increase of heat according to the depth in the earth. 



We find, next to elevated points, subsidences of equal 

 value in the contrary way. Considering in this way the 

 different elevations in different periods, we find that the 

 greatest appeared latest. But it must be observed that 

 the latest elevations must frequently have taken place upon 

 already vaulted places, or even on those which have been 

 more than once elevated. Besides the actually highest chains 

 are those the least destroyed, and in uniting them with the 

 first formed, may possibly not have been elevated more, or 

 may have changed entirely their aspect by frequent subse- 

 quent elevations. If the latest elevations have produced the 

 greatest protuberances, a similar complicated relation must 

 have taken place for the subsidences. In the primitive time 

 the sea was not so deep as now ; this depth increased gradu- 

 ally till our times, when the hydrographic value equalled 

 those got by the hypsometry of our highest hills. 



Can we calculate the numeric value of the vaults of a 

 country and its relative subsidences ? 



It becomes much more difficult to determine the subsidences 

 which may be produced by the inversion of beds. If one had 

 only one series of beds, elevated in a straight line, we should 

 determine the angle of inclination, the thickness, and the ex- 



