94 Mr. J. Ball on tfie Formation of 



I might here close these remarks, which are directed rather 

 to combat what appears to me excessive in recent theories, than 

 to attempt a complete explanation of the origin of alpine valleys 

 and lakes. Probably the time is not yet come for a solution of 

 the difficulties connected with this great problem ; but a writer 

 with no scientific reputation to defend, who has often been led 

 to reflect on the subject in the presence of those great monu- 

 ments of the past history of the earth that survive in the Alps 

 and in other mountain districts, may throw out for future dis- 

 cussion the result, though confessedly incomplete, of his own 

 efforts to account for the phenomena. 



I may mention that my ideas on this subject have been formed 

 in all but utter ignorance of the views of those geologists who 

 have maintained opinions somewhat similar, and in particular of 

 those of Constant Prevost and Dana. I am very imperfectly 

 aware of the progress of speculation even at present in the 

 same direction ; but it seems to me that, while both the writers 

 above-named, and several others, have proceeded in the right 

 track, they have not followed out the fundamental conception 

 with the requisite strictness to its legitimate consequences. That 

 the earth has gradually cooled down from a previous high tem- 

 perature during the period which has intervened between the 

 earliest geological record and the latest tertiary epoch, and that 

 by a necessary consequence it has diminished in volume during 

 the same period, is the belief of many, probably of nearly all 

 geologists. This hypothesis, duly followed out, leads us towards 

 an explanation of the origin of mountain chains, and the cor- 

 related depressions, which, if not quite complete, appears to me 

 far more satisfactory than any other, and readily applicable to 

 the leading points of the orography of the Alps. Those who 

 have speculated on the subject seem to me to have erred in look- 

 ing to local subsidence as the chief mechanical result of con- 

 traction by cooling, and more especially when they have supposed 

 certain areas of the earth's surface to have been, in a special and 

 exceptional sense,, areas of cooling. 



The postulates which may, as I think, be justly assumed for the 

 purpose of reasoning on the hypothesis in question are these : — 



1. From the period when organic life commenced on the sur- 

 faceof our planet, the outer portion of the crust must have assumed 

 a temperature not far removed from that which it now possesses, 

 and which depends mainly upon the ratio between the heat re- 

 ceived from the sun and that lost by radiation. 



2. The inner portion of the crust, and the nucleus, usually 

 supposed to be viscous or fluid, being cooled with extreme slow- 

 ness by conduction, would contract much more than the outer 

 surface of the spheroid. 



