Miscellanien. 411 



5. The existing atmospheric agents and other causes, are con- 

 stantly changing the condition of the surface of the globe. 



Mr. Babbage then proceeds to remark, that whenever a sea or 

 lake is filled up, by the continual wearing down of the adjacent 

 lands, new beds of matter, conducting heat much less quickly than 

 water carries it, are formed ; and that the radiation also, from the 

 surface of the new land, will be different from that from the water. 

 Hence any source of heat, whether partial or central, which previ- 

 ously existed below the sea, must heat the strata underneath its bot- 

 tom, because they are now protected by a bad conductor. The 

 consequence must be that they will raise, by their expansion, the 

 newly formed beds above their former level ; and thus the bottom 

 of an ocean may become a continent. The whole expansion how- 

 ever, resulting from the altered circumstances, may not take place 

 until long after the filling up of the sea ; in which case its conver- 

 sion into dry land will result partly from the filling up by detritus, 

 and partly from the rise of the bottom. As the heat now pene- 

 trates the newly formed strata, a different action may take place ; 

 the beds of clay or sand may become consolidated, and may contract 

 instead of expanding. In this case, either large depressions will 

 occur within the limits of the new continent, or, after another inter- 

 val, the new land may again subside and form a shallow sea. This 

 sea may be again filled up, by a repetition of the same process as be- 

 fore, and thus alternations of marine and fresh water deposhs may 

 occur, having interposed between them the productions of dry lands. 



Mr. Babbage's theory may be thus briefly stated — 



In consequence of the changes actually going on at the earth's 

 surface, the surfaces of equal temperature within its crust, must be 

 continually changing their form, and exposing thick beds near the 

 exterior, to alterations of temperature — the expansion and contrac- 

 tion of these strata will probably form rents, raise mountain-chains, 

 and elevate even continents. 



The author admits that this is an hypothesis ; but he throws it 

 out, that it may be submitted to an examination, which may refute 

 it if fallacious — or if it be correct, establish its truth — because he 

 thinks that it is deduced directly from received principles, and that 

 it promises an explanation of the vast cycles presented by the phe- 

 nomena of geology. 



