and Orography of the Earth? s Surface. 303 



been so much forced from their former position between the 

 new vaults, as to have preserved a compression upon them. 

 Those meridian-like subsidences must have had a tendency 

 to produce only in N.S. direction, long and oval basins, and 

 not circular ones, in E.W. direction ; which, on the contrary, 

 was always the case between two equatorial elevations. The 

 Mediterranean is an example of the last. Finally, we must 

 add the fact which concords with the rotation of a body whose 

 interior is igneous, viz., the arches or higher parts of the 

 earth's body, formed in consequence of the centrifugal force, 

 are parallel to each other, but no one of these goes entirely 

 round the earth as a continued line. The Alps, Taurus, 

 Himalaya, and the chains of Central Africa, are examples of 

 this kind. 



Is it not possible to estimate the value of the various eleva- 

 tions and subsidences on the earth's surface, at different 

 periods of time ? 



It is possible, — but our knowledge in astronomy, physics, 

 and geology is still too imperfect to allow of more than an 

 approach to the answer. 



Let us take the simplest case of an island composed of 

 horizontal marine beds. We would measure the depth of 

 the sea and the height of the highest mountain of the island, 

 add these together, and then endeavour to ascertain whether 

 the sea subsided, or the land elevated. As to the last con- 

 clusion there remains the question, Does the sea bottom still 

 preserve its original height \ This shews us the necessity 

 of having a knowledge of the normal depth of all seas in the 

 primitive time, so that, according to our knowledge of Batho- 

 graphy, and the whole quantity of water on the earth, we 

 might then limit per maxima and minima the same value for 

 the various periods. This done, we could then calculate each 

 elevation. 



Let us now take the case of an island of a roof-like form, 

 where we shall have the elevation of the summit of the roof, 

 we could also obtain the elevation of each isolated parts of 

 its inclined phases. 



If the island is long, with a steep inclination on one side, 

 and a very slightly inclined plane on the other, as for instance, 



