resum:^ and general discussion. 391 



with the later geological hi.stoiy of that region have been already pre- 

 sented and commented on to the full extent which the space at the writer's 

 command has permitted. That the ice sheet extended mnch farther 

 beyond the base of the range than was the case in the Alps, cannot be 

 doubted. The occurrence of the asar forms a marked feature of Scandinavian 

 glacial geology, not paralleled in the slightest degree by anything seen in 

 the Alpine region, and in regard to the explanation of which the most 

 discordant opinions have been and still are held by those who have devoted 

 much time to their examination. Even in the Scandinavian Range, however, 

 we have still i-eraaining extensive nece fields, with numerous large glaciers 

 issuing from them, while the striation over regions now abandoned by the 

 ice seems to point unmistakably towards the axis of the still partly glaciated 

 range, as has been set forth in the preceding pages. We thus find ourselves, 

 in discussing the phenomena of the Scandinavian Glacial epoch, guided 

 by present conditions to such an extent that we have but little diffi- 

 culty in recognizing the general sequence of events, the details of which 

 have been worked out with so much care and skill by the Swedish Geo- 

 logical Survey. 



We next pass to a region where the Glacial phenomena exhibit the high- 

 est degree of complexity. We are beset with difficulties when we attempt 

 to solve the problem presented by the Northern Drift in Northeastern 

 America. It is indeed remarkable what dissimilar conditions are presented 

 on the two opposite sides of this continent ; but the complications of our 

 Drift region have already been the subject of sufficient comment, and we need 

 not enlarge farther upon them. Absence of a definitely known centre of 

 glaciation ; extreme complexity in the direction of the striation ; proofs of 

 the former presence of the sea over a part of the region, and of fresh water 

 over another extensive portion ; enormous accumulations of detrital material 

 evidently deposited by water ; occasional peculiar transportation of boulders 

 in a manner not in harmony with anything we see ice doing at the present 

 time ; occurrence of linear accumulations of sand, gravel, and boulders 

 closely resembling the asar in character ; proofs in some parts of the Drift 

 region of the prevalence during the Glacial epoch of a colder climate, and 

 in others of one warmer than that now existing — these are some of the diffi- 

 culties which must be met by those who undertake to solve the problem 

 of the Northern Drift of Northeastern America. That the assumption of a 

 lower mean temperature of the earth would be of no assistance to the 



