410 Captain F. W. Hutton on the Phenomena of the 



movements of the surface can be accounted for. For example, 

 the Gulf-stream carrying a high temperature into northern lati- 

 tudes may be the cause of the recent elevation of Sweden, while 

 the cold arctic current sweeping down through Davis^s Straits 

 may be the cause of the depression of Greenland*; for on a 

 spherical surface contraction would cause depression by decrea- 

 sing the lateral thrust and throwing more weight on to the un- 

 derlying superheated rocks. Again, if, as explained by Mr. Croll, 

 the earth should enter upon a cold period, all land of a higher 

 mean temperature than 32° would have a tendency to sink, while 

 that previously covered by snow or ice would not be affected, 

 thus helping to increase the cold. The submergence of a large 

 part of North Wales daring the glacial period, and its subsequent 

 reemergence, may perhaps have been owing to the cold of the 

 period itself, followed by a return to its original temperature. A 

 difference in temperature of about 10° would be sufficient to 

 effect this. South Sweden was also depressed when the cold 

 was most severe, and has since been raised more than 200 feet. 

 I will now proceed to consider the second cause of oscillations, 

 viz. the alteration of pressure by the denudation and deposition 

 of rocks. In this case, unfortunately, I cannot make even ap- 

 proximate calculations as to the weight of deposits necessary to 

 cause movement, in consequence of our ignorance of the rigidity 

 of the outer crust of the earth. We certainly know that this 

 rigidity is sufficient to overcome the attraction of the moon ; but 

 as this force acts only for very short periods in the same direc- 

 tion, the inertia of the rocks will help to supplement the rigidity ; 

 so that I do not see how even a minimum quantity can be ob- 

 tained for it. Every geologist, however, knows many facts 

 proving that all thick formations have been deposited during 

 subsidence ; and the fossils in these formations often prove that 

 the subsidence has been about equal in rate to the deposition, 

 and also that in most (if not all) cases high land has been not 

 very far off. Now it is highly improbable that the rate of depo- 

 sition and subsidence should coincide so often unless one was 

 caused by the other; and as we know from a priori reasoning 

 the great probability there is of an increase of pressure causing 

 subsidence, we may, I think, safely assume that such is the case. 

 What, then, would be the effects resulting from this cause? 

 Wher>e denudation was going on, the mass of land would be les- 

 sened ; but, as already stated, the rate of denudation is much 

 slower than the conduction of heat through rocks, consequently 

 the isogeothermals would recede as fast as the denudation went 



* The climate of Greenland is known to have decreased in temperature 

 during the last 900 years. See ' The Land of Desolation/ by I. J. Hayes, 

 M.D. London, 1871. 



