310 M. Ami Boue on the Palozoliydrography 



On the other hand, as the cavities of the earth's surface 

 are in time in relation with their chains and protuberances, 

 we ascertain by this a mean to determine for each geological 

 period the greatness at least of the median value of the ele- 

 vations ; not only for the general one as vaults, hut also for 

 the more particular as cliains, and that through the median 

 value not only of the greatest subsidences, but also through 

 that of the deepest rents in the sea bottom. 



We can say the following : — When we find for a sea a cer- 

 tain medium of depth, which has a determined value of sur- 

 face, and a determined quantity of water, what medium of 

 depth will another sea have with another value of surface 

 and quantity of water ? When we have got this medium 

 depth or medium value of subsidences, we can positively 

 deduce from it the medium value of the elevations. 



But the medial value and the place of the greater pro- 

 tuberances of the earth's surface are in constant relation 

 with the height of the greatest chains and their places on 

 the earth's surface ; so that we have a mean to conclude 

 something approximatively for the chains, which may pos- 

 sibly surpass the medium value of the elevations in each 

 period. This is enough to shew how important are such de- 

 terminations of orographical medium value, as they were 

 traced by Humboldt, Strantz, Berghaus, and others. 



Some may object that we shall never either know the true 

 place of lands and seas, nor the greatest elevations and sub- 

 sidences in the various geological periods, notwithstanding 

 we may arrive at the knowledge of the medium value of the 

 elevations and subsidences, as well as at that of the sea 

 depth. Our physical and astronomical knowledge is truly 

 not yet sufficient for it, but geology seems to give hope 

 for the solution of the problem. I would, for instance, ex- 

 pect a natural result when one remembers that subsidences 

 are always in the neighbourhood of the elevations, or 

 vice versa, as in the see-saw ; one would determine the 

 rest by traces left of the one or other of these events. 

 Secondly, one must employ Leblanc's doctrine of the con- 

 stant opposition in the directions of two events of the kind, 

 which follow one another, and apply this to all the events of 



