On Theories to account for Glacial Submergence. 337 



pure copper, and pure nickel has about ten times the resist- 

 ance ; but at the temperature of liquid oxygen boiling at 

 ordinary atmospheric pressure, the specific resistance of iron 

 is only two-thirds of that of pure copper at the ordinary tem- 

 perature, whilst that of nickel is only about twice as great as 

 that of iron. It is a striking illustration of the effect of great 

 cold on electrical conductivity to realize that at the tempera- 

 ture of boiling liquid oxygen pure iron conducts electricity 

 better than the purest electrolytic copper does at ordinary 

 temperatures. We hope before long to extend and complete 

 the above investigation. 



August 1892. 



nee, 



XXXVIII. On Theories to account for Glacial Submerge 

 By Rev. 0. Fisher, M.A., F.G.S.* 



GEOLOGISTS who have made glacial epochs their special 

 study have in general come to the conclusion that the 

 advent of an ice-sheet has been accompanied by a considerable 

 depression of the earth's surface in the regions covered by it. 

 More than one theory has been advanced to account for this 

 circumstance, and we will begin by examining what appears 

 to be the latest conception upon the subject, but one which 

 has not hitherto been submitted to the test of numerical 

 computation. 



It is easy to see that if an area not previously within the 

 influence of perpetual frost becomes newly enveloped in ice, 

 a corresponding cooling of the ground must be the conse- 

 quence, and a depression of the isogeotherms accompanied by 

 a contraction of the rocks must follow. The idea that this 

 contraction may possibly account for much, if not the whole, 

 of the depression which requires to be explained, appears to 

 have presented itself to some glacialists. The following cal- 

 culation has been undertaken with the view of testing this 

 hypothesis. The result will show that it is wholly inadequate 

 to explain the phenomena. 



We may consider that before the ice-sheet was formed the 

 underground temperature increased proportionally to the 

 depth, as, for instance, one degree Fahr. for 51 feet. In 

 that case the temperature-curve will have been a straight 

 line, and may be expressed by 



v =a mx + b ; 



where v is the temperature at the depth #, m the rate of in- 



* Communicated by the Author. 



