208 the Canadian naturalist. [May- 



through, colder regions of space ; or shiftings of the earth's axis ; 

 or alteration in the heat-conducting power of the atmosphere, 

 would leave, I apprehend, a more uniform distribution of climatic 

 results, and obliterate those delicate proportions of species, varying 

 in different beds of the same epoch, in exact analogy to those 

 variations produced by the causes now at work. To account for 

 the fact we are examining, there must have been a deflection of 

 the Gulf Stream from our coasts. The effect of the Gulf Stream 

 is shown by the lingering of a species like Saxicava (Panopaea) 

 Norvegica upon the Dogger bank, which is protected from its 

 influence, and subject to an arctic current, while it is extinct on 

 the west of Scotland. Moreover, the existence of Pect&n Islandicus 

 in its natural position over large beds in the glacial clay, combined 

 with the fact of its total absence, not only from our present sea, 

 but from any intermediate bed, renders its comparatively sudden 

 extinction by warmer currents taking the place of the more arctic, 

 the most probable hypothesis. The cause of extinction must have 

 been quiet, or its position would not have been so natural, and at 

 the same time sufficiently marked to permit little lingering. The 

 deflexion of the Gulf Stream must be considered in connection 

 with those movements of the land which we know to have been 

 going on in Scotland during the whole epoch. The subsidence 

 indicated by the shell beds at Airdrie and elsewhere was followed 

 by an elevating movement, which, judging from the peculiarly 

 undisturbed arrangement of different clays in various uplifted 

 beds, must have been very gradual. This elevating movement 

 itself also, is proved by the sections given by Mr. Jamieson* to 

 have been broken by a second, although slighter subsidence. The 

 shifting arrangements of the boundaries of land and water, 

 occasioned by these undulations of the earth's crust, would 

 materially affect climate, distributing variously the points of 

 insular and more continental temperatures, and in connection with 

 the deflection of the Gulf Stream, would (I am at present disposed 

 to think) sufficiently account for the cold of the glacial epoch. 

 Upon this point, however, Mr. Croll's most able and remarkable 

 papers give him a right to be heard, and I would venture to 

 suggest to him the consideration of the variable eccentricity of the 

 earth's orbit (as claimed by his theory) upon the climate of 

 Canada, so as to account for the fact that its temperature was, 



* Journal of Geological Society, Vol. xxi. 



