574 Dr. Ricketts — On the Cause of the Glacial Period. 



of subsidence and accumulation co-existing in the different forma- 

 tions,— on the existence of bays and of deltas at the mouths of all 

 great rivers, being the submerged and filled-up continuation of their 

 valleys ; in the latter the result of artesian borings has proved the 

 occurrence at various depths of evidences of what have been succes- 

 sive land surfaces, — on the depression which took place during the 

 Glacial Period, and the partial re-emergence of the land when it was 

 relieved of its weight of ice and snow, — and on the subsidence 

 recently occurring in Greenland simultaneously with a rapid increase 

 of accumulation of snow. 



The occurrence of subsidence of land being due to the pressure 

 of accumulations, though it has been advocated by Sir John Herschel, 

 by Prof. Hall of New York, and by Dr. Dawson of Montreal, appears 

 in a singular manner to have escaped the consideration of geologists ; 

 though by this circumstance only can a satisfactory explanation be 

 given of many geological phenomena. Nevertheless, the fact of their 

 simultaneous occurrence is constantly recognized. 1 



The relative positions under which the two Poles are placed are 

 so different, that great care must be taken in arguing from the state 

 of one 'to that of the other. It must not be inferred that because it 

 may be possible that the land, situated at the South Pole and sur- 

 rounded by water, is covered with an " ice-cap," that therefore the 

 ocean, situated at the North Pole and surrounded by land, would be 

 covered in the same way. It appears to be more than doubtful 

 whether, with the existence of an Arctic Ocean having communica- 

 tions open with the Atlantic and Pacific, an " ice-cap " comparable 

 with that covering the land about the Antarctic Pole could by any 

 possibility exist ; for before a resting place could be found sufficient 

 to bear such an accumulation of snow, as has been supposed to have 

 at one time existed, the whole sea must have been frozen even to 

 its lowest depths ; and that could not take place whilst salt water 

 continues to get denser as it becomes colder, and there is also a free 

 communication between the Polar Sea and the Atlantic. 



Nor could there have been, during the Glacial Period, any great 

 thickness of snow on the land surrounding the Arctic Sea ; for per- 



1 In the President's Address to the Geologists' Association, Nov. 7th, 1873, Mr. 

 H. Woodward, F.B, S., has objected to the theory of subsidence being the result of 

 accumulation, on the grounds that if in the Bay of Bengal (where, by the artesian 

 borings made in the Delta of the Ganges, the land has been proved to have sunk to 

 the depth of 481 feet and upwards) the sediment deposited has power by gravitation 

 to thus depress the ocean-bed, much more ought the solid mass of the Himalayan 

 range, with its innumerable and lofty peaks, to sink into the yielding crust beneath 

 (Geol. Mag. 1873). But the areas out of which the Himalayas have been sculptured 

 have, from the commencement of their present denudation, been sustained above 

 the sea-level, and the weight to be supported has diminished, as particle after particle 

 has been removed, the peaks and valleys registering a portion, but by no means the 

 greater amount, of the denudation the mass has undergone ; so that the Himalayas, 

 in consequence of the great amount of denudation to which they have been subjected, 

 will not press with so great a weight upon the fluid substratum. But if the 

 sediment brought down by the Ganges and Brahmapootra has caused, by its weight 

 that subsidence which has taken place in the Bay of Bengal, it necessarily follows 

 that the area, forming and supporting these mountains, must rise in accordance with 

 the amount of material removed. 



