February 19, 1892.] 



SCIENCE. 



107 



PEOFESSOE GEIKIE ON THE GLACIAL PEEIOD. 



On Nov. 12 the Edinburgh Geological Society held its 

 anniversary meeting, at which Professor Geikie delivered 

 his presidential address, the subject being, " Supposed Causes 

 of the Glacial Period." Tlie lecturer began by remarking 

 that, although the subject of his address had frequently been 

 canvassed, the last word had not yet been said. The ques- 

 tion of the cause or causes of the Ice Age was indeed a hard 

 one, and he was not going to advance any novel speculation 

 or hypothesis on the subject. His object was rather to ex- 

 amine certain views, which, after having been abandoned as 

 untenable, had again been put forward to account lor the 

 phenomena of the glacial period. Before attempting to 

 criticise these views it was obviously necessary to ascertain, 

 in the first place, what conclusions had been arrived at with 

 regard to the climatic conditions of glacial or Pleistocene 

 and post-glacial times. We must first have an adequate 

 conception of those conditions before we could estimate the 

 value of any theory of their origin. The climatic conditions 

 of the Pleistocene were then considered. It was shown that 

 at the climax of the so called glacial period the line of per- 

 ennial snow in Europe was depressed for not less than 3,500 

 feet on an average. To bring about such a depression the 

 mean annual temperature must have been lowered 10* or 

 thereabout. 



Full consideration of all the glacial phenomena led to the 

 following conclusions: (1) That the cold of the glacial pe- 

 riod was a general phenomenon due to some widely acting 

 cause — a cause sufficient to influence contemporaneously 

 the climate of Europe and North America. (2) That gla- 

 ciation in our continent increased in intensity from east to 

 west, and from south to north. (3) That where now we 

 have the greatest rainfall, in glacial times the greatest snow- 

 fall took place. (4) That in the extreme south of Europe, 

 and in North Africa and South-western Asia, increased rain- 

 precipitation accompanied lowering of temperature — from 

 which it might be inferred that precipitation in glacial times 

 was greater, generally, than it is now. 



The remarkable climatic changes of the glacial or Pleisto- 

 cene period were next considered. It had been proved that 

 the period was interrupted certainly once — perhaps, as many 

 geologists maintained, at least twice — by what were known 

 as inter-glacial conditions. The evidence of this was treated 

 in considerable detail, and the character of the inter-glacial 

 climate was described as being markedly temperate and gen- 

 ial. There could be no doubt whatever that the Pleistocene 

 period was characterized by great oscillations of climate — 

 extremely cold and very genial conditions alternating. The 

 " ' -^ ''kewise that these 



post-glacial times changes in the reiauw, _ 

 sea had taken place. 



Any suggested explanation which did not fully account 

 for these various climatic and geographical conditions could 

 not be satisfactory. The view which had met with consid- 

 erable acceptance, especially by American geologists, was 

 that which attributed the phenomena of glacial times to great 

 movements of the earth's crust. Professor Geikie then pro- 

 ceeded to examine that " earth- movement hypothesis" in 

 detail. He pointed out that in the first place there was not 

 the least evidence of great continental elevations in the 

 northern hemisphere, such as the hypothesis postulated. 

 Next, be showed that even if the desiderated earth-move- 



ments were admitted, they would not account for the phe- 

 nomena. Each of the several applications of this earth- 

 movement hypothesis was criticised in succession, with the 

 result that they were all found inadequate. Neither great 

 elevation of the northern lands alone, nor such elevation 

 accompanied by submergence of the Isthmus of Panama and 

 the deflection of the Gulf Stream, would account for the pe- 

 culiar conditions of the Ice Age. These changes, no doubt, 

 would profoundly affect the maritime regions of North 

 America and Europe, but they would not reproduce thecon- 

 diticns that obtained at the climax of the Ice Age. Another 

 objection to the earth-movement hypothesis was this, that it 

 did not account for inter-glacial conditions. The advocates 

 of that hypothesis imagined that those conditions would su- 

 pervene when the highly-elevated northern regions were de- 

 pressed to their present level, and when the Isthmus of 

 Panama reappeared. But these were precisely the conditions 

 that obtained at the present time, and yet in spite of them 

 the climate was neither so equable nor so genial as that 

 which obtained in inter-glacial times and during the mild 

 stage of the succeeding post-glacial period. The earth- 

 movement hypothesis must be rejected, not only because it 

 was highly improbable that such wonderfully rhythmic 

 elevations and depressions of high northern lands and of the 

 Isthmus of Panama could have taken place, but chiefly be- 

 cause it did not explain the conditions of the glacial period, 

 while it practically ignored those of inter-glacial times. 



Professor Geikie next considered the proofs of former sub- 

 mergence which are so abundantly met with in temperate 

 and northern latitudes, and discussed the various views 

 which have been advanced to account for the facts. He 

 concluded his address by considering an objection which had 

 been urged against the physical theory of the glacial period 

 as advocated by the late James Croll. This objection was 

 based on certain estimates of the rate of erosion of river- 

 valleys, the accumulation of alluvial deposits, and so forth, 

 from which it was sought to show that only some 7,000 or 

 10,000 years had elapsed since the close of the glacial period. 

 The consideration that, if this contention were true, it would 

 bring the close of the Ice Age down to the dawn of civiliza- 

 tion in Egypt was rather startling, to say the least. The 

 fact was, however, that all such estimates, however carefully 

 made, were unreliable. Dr. CroH's theory might some day 

 be supplanted by one more satisfactory, but it would not be 

 overturned by niggling and inconclusive measurements of 

 that kind. That theory holds the field in giving the sim- 

 plest and most consistent interpretation of the climatic vicis- 

 situdes of the Pleistocene and post glacial periods, while it 

 is the only one that throws any light on the very remarka- 

 ble conditions that obtained during inter-glacial times. 



■"^ERS TO THE EDITOR. 



ed to be as brief as possible. The writer's name 

 f of good faith. 

 Lf/fc . ..^ . hundred copies of the number containing his 



communication witt l.^., .. hedfree to any correspondent. 



The editor will be glad to publish any queries consonant with the character 

 of the journal. 



The Loup Rivers in Nebraska. 



Permit me to submit through your columns to Professor Hich;.: 

 the following questions and comments on his acceptable account 

 of the Loup and Platte Rivers in Science for Jan. 29 last. 



The topographic maps of the region in question are too incooi ■ 

 plate for one to learn much from tbem concerning the prest-nt 

 condition of the river valleys ; but from general description ^ of 

 that part of the country and from the brief mention by Profe-ssor 

 Hicks of the " channels excavated from fifty to two hundrec^ feet 



