July 13, 1893] 



NA TURE 



24: 



But most of the examples were from localities where 

 I the included fragments had been crushed against one 

 another by earth movements, the grooves running alike 

 li across the included pebbles and the matrix in which they 

 (were imbedded. Or they were from the neighbourhood 

 ! of what had been mountain ranges repeatedly through 

 j long ages. Even if we admit that some ancient con- 

 Iglomerates appear to have derived their boulders from 

 I glacial debris, that does not make the conglomerates 

 : glacial, but only requires glaciers in the adjacent moun- 

 tains then as now. On the hypothesis of the geographical 

 origin of glacial conditions, seeing that there must have 

 been elevations and submergences over and over again, 

 glacial phenomena should recur near the areas of up- 

 ' heavaljOnly without that periodicity which is required by 

 the astronomical theory. There is, moreover, in the 

 fossil flora and fauna no evidence of the recurrence of 

 widespread glaciation such as would justify our referring 

 it to a glacial epoch. 



The astronomical glacialists further hold that not only 

 were there secularly alternating periods of cold and heat 

 in either hemisphere throughout the ages, but that within 

 each period there were shorter periods of greater and less 

 intensity of cold, of which we find evidence in the so- 

 called interglacial beds of Britain, and in such deposits 

 :is those of Dtirnten, where glacially striated pebbles 

 underlie lignite which is covered also by morainic debris. 

 But all advocates of the geographical explanation sup- 

 pose that the earth movements on which it depends were 

 discontinuous and subject to considerable oscillation, 

 while the advance and retreat of glaciers, as a mere 

 weather result, is so marked that we may safely admit 

 that, as a climatic result of oscillitions of level, it might 

 be quite as great as required by any of the cases referred 

 to. 



Croll says that by far the most important of all the 



agencies, and the one which mainly brought about the 



, glacial epoch, was the deflection of ocean currents, but he 



does not show that it is not possible to account for this 



deflection by earth movements. 



There is one very important fact which does not seem 

 to be generally recognised, namely, that the last glacial 

 conditions extended only over a limited area on either 

 side of the North Atlantic, and that this limitation must 

 be referred to geographical causes, so that, if these were 

 sufficiently powerful to determine the area, they may 

 account for the glaciation itself. " What is wanted, how- 

 ever," our author remarks, "is not testimony to sporadic 

 glaciers or local ice action, but to widespread glacial 

 phenomena such as would witness an ice age." 



The absurdity of the answer that percolating water 



; must have removed ice markings from the surface of the 



( stones is sufficiently obvious to any one who has had his 



j attention called to the much finer markings on fo,sils, 



&c , which have been preserved. 



The grooved stones of Devonian Age in Victoria are 

 ' rih about as much as the facetted stones from Gorplitz 

 1 by Barna, which are supposed to prove the great southerly 

 j extension of glacial action in Germany, but which more 

 I probably owe their form and condition to blown sand. 

 ! Several ingenious explanations have been offered of the 

 [occurrence of marine shells in stratified drift on the high 

 ; ; ground of southern Sweden and northern England and 

 ! NO. 1237. VOL. 48] 



Wales. The more obvious explanation is, of course, that 

 they were left there as the shingly shore of the receding 

 post-glacial sea. But this would have involved earth 

 movements in comparatively recent times to so great an 

 extent as would lend probability to the theory of such 

 elevations as would account for glaciers in temperate 

 regions, and of such submergences as would explain the 

 widespread post-glacial sands and gravels. Some there- 

 fore suggested that these masses had been scraped up 

 from the sea bottom and been pushed up the mountains to 

 their present position ; that they were, in fact, part of a 

 great terminal moraine of the polar ice-sheet. ." ome got 

 over the difficulty of explaining the even stratification 

 and the ripple marks on the beds, as well as the non- 

 Arctic character of the shells, by supposing that the 

 sand and shells were pushed up in the ice from the 

 sea bed in temperate regions, but that the deposit in 

 which they are now seen was washed from the ice-foot at 

 these several elevations by the fresh water due to the 

 melting of the ice, and bearing away with it the mud, 

 sand, and stones transported so far in the ice. 



Too much stress must not be laid upon stratification and 

 lines of boulders in the drift, as this may be produced by 

 iceberg loads being thrown down in deep water ; just as 

 when a handful of mixed sand and grit of various form and 

 different coarseness is dropped into a long glass of water, 

 the larger grains will, cateris paribus, reach the bottom 

 first, and a rough stratification will be produced. The 

 contortion of clays and sands can often be explained by 

 the loads of debris carried by icebergs and dropped upon 

 them, squeezing the underlying plastic mass away, and 

 rolling up the surrounding layers in every variety of fold 

 and crumple. 



Our author lays great stress on the fact that there is 

 now no polar ice-cap at all, and that all the evidence 

 shows that the pole is not, and never has been, the centre 

 of greatest cold or of greatest glaciation. The ice 

 radiated from Scandinavia, not from the pole, and the 

 pillars and prominent unglaciated rocks of Northern 

 Asia show that there has been no ice sheet there in recent 

 ages. 



In his advocacy of a considerable submergence in 

 comparatively recent times our author has the support of 

 Prof. Prestwich, who, in the last number of the Proceed- 

 ings of the Royal Society, has expressed the opinion that 

 the masses of unstratified rubble commonly found resting 

 on the slopes and terraces along the English Channel 

 seem to be due to a force of propulsion for which the 

 hithei'to generally-suggested causes are manifestly inade- 

 quate. He extends his generalisation over Western 

 Europe and the coasts of the Mediterranean, and arrives 

 at the conclusion that the loess was a sediment deposited 

 from the turbid sea-waters during the submergence, while 

 the superficial deposits called " head " he refers to the 

 surface debris swept ofif by divergent currents during the 

 subsequent upheaval. Both of these movements he 

 refers to periods of such short duration that large 

 ni mbers of animals were simultaneously drowned and 

 tl e waters were rendered so turbid as to be unsuited for 

 n arine life. 



Our author explains many of the phenomena of the 

 later drift by reference to a great submergence, but, wish- 

 ing apparently to imply that it was of a still more 



