340 ANNUAL REPORT .SMITHSONIAN INSTITUTION, 1908. 



unanimously indicate that all great climatic changes have occurred 

 simultaneously on the whole earth." « 



But geological opinion is by no means unanimous on this ques- 

 tion, that the major climatic variations were world-wide in their 

 influence. The amplest evidence in suj^port of the view that a colder 

 climate was once universal is supplied by the Pleistocene glaciations; 

 and it is certain that at one part or another of the Pleistocene period 

 the glaciers of many distant parts of the world were much larger, and 

 that wide areas in the north temperate zone were overwhelmed Ijy 

 glacial conditions. But there appears to be a steadily growing opin- 

 ion that the glaciers of the different glacial centers did not attain 

 their greatest development at the same time. Thus, the glaciation of 

 Greenland is now at its maximum^ at an earlier period of the Pleisto- 

 cene Labrador was covered by an ice sheet, which dwindled as that 

 of Greenland developed ; and the glaciation of the Canadian Rocky 

 Mountains was probably still earlier than that of Labrador. Sim- 

 ilarly' in Europe the conditions of preservation and general aspect of 

 the glacial deposits suggest that the culmination of the Norwegian 

 glaciation was somewhat later than that of the British Isles. 



The General Uniformity of Cliiniates in the Past. 



The first striking fact in the geological history of clim.ate is that 

 the present climate of the world has been maintained since the date 

 of the earliest, unaltered, sedimentary deposits. The oldest sand- 

 stones of the Scotch Highlands and the English Longmynds show 

 that in pre-Cambrian times the winds had the same strength, the 

 raindrops were of the same size, and they fell with the same force 

 as at the present day. The evidence of paleontology proves that the 

 climatic zones of the earth have been concentric with the poles as far 

 back as its records go ; the salts deposited by the evaporation of early 

 Paleozoic lagoons show that the oldest seas contained the same ma- 

 terials in solution as the modern oceans; and glaciations have re- 

 curred in Arctic and, under special geographical conditions, also in 

 temperate regions at various periods throughout geological time. 



The mean climate of the world has been fairly constant, though 

 there have been local variations Avhich have led to the development of 

 glaciers in regions now ice free, at various points in the geological 

 scale. That there has been no progressive chilling of the c*iirth since 

 the date of the oldest known sedimentary rocks is shown b}' their 

 lithological characters and by the recurrence of glacial deposits, some 

 of which were laid down at low levels at intervals throughout geolog- 



''Dr. Nils Ekholm, "On the variations of the climate of the geolosiciil and 

 historical past and their causes," Quart. Journ. Roy. Met. Soc, Vol. XXVII, 

 1001, 1). 3, 



