354 PKOCEEDINGS O:? THE GEOLOGICAL SOCIETY. [JuilG 9, 



they do now from the glaciers of Greenland. "We have plenty of 

 evidence of iceberg action during the glacial period. 



I believe I have shown that glaciation depends chiefly on a cold 

 summer, but partly also on an abundant snow-fall. I have now to 

 show that a period of cold summers, caused as I have explained, 

 must be also one of snowy winters; so that the two conditions 

 favourable to glaciation will occur together. 



During the mild winter of the glaciated hemisphere, there is a 

 hot summer in the opposite one. Increase of temperature promotes 

 increase of evaporation in a much greater ratio than that of the 

 increase of temperature ; and increased evaporation in the summer 

 hemisphere wiU produce increased snow-fall in the winter one. We 

 know that at present the vapour raised in one hemisphere is to a 

 great extent precipitated in the other; for, were it not so, the 

 southern hemisphere, by reason of its greater extent of ocean sur- 

 face, would have a rainier climate than the northern ; and such does 

 not appear to be the case on the whole. Besides, during a glacial 

 period, the atmospheric circulation between the two hemispheres, at 

 the time of the earth's minimum distance from the sun (which on 

 my theory was in the winter of the glaciated hemisphere), must be 

 more active than ever it is now ; for when the earth, at either sol- 

 stice, was nearer the sun than is ever the case now, and the differ- 

 ence of temperature between the two hemispheres consequently at 

 its greatest possible amount, this would produce a very active circu- 

 lation of atmospheric currents between the two hemispheres, which 

 would involve the deposition as rain or snow in the winter hemi- 

 sphere of a great part of the moisture evaporated in the summer one. 



Some interesting collateral observations remain to be made. 



I believe that the foregoing remarks furnish the explanation of a 

 very remarkable fact in physical geography. Not many coasts in 

 the world are cut up into fiords ; and aU, or nearly all, that are so, 

 are western coasts in high latitudes. The fiord formation is found 

 in North- western Europe, including Norway, the west of Scotland, 

 and the west of Ireland, in North America from Yancouver's Island 

 northwards, and in South America from the island of Chiloe south- 

 wards. From Vancouver's Island to Chiloe. is an immense stretch 

 of nearly straight coast-line ; but at those limits its character changes 

 quite abruptly. The transition from straight to indented coast-lines 

 coincides pretty nearly with that from dry to moist climates ; and 

 the change from the dry climate of Chile to the moist one of western 

 Patagonia is accompanied, as we might expect, by a great depression 

 in the snow-line on the Andes. (See tabular statement above.) It 

 is now generally believed that the prevalence of lakes in high lati- 

 tudes is, in some way, a result of glacial action ; it can scarcely be 

 doubted that this is equally true of fiords ; and the coasts I have 

 mentioned are those on which glacial action must necessarily be the 

 most energetic, because west coasts, in high latitudes, are exposed 

 to west winds (Maury's " countertrades "), which deposit on the 

 mountains in snow the moisture they have taken up from the sea. 



Geologists appear to be now agreed that the carboniferous climate 



