250 PROFESSOR JAMES GEIKIE, LL.D., D.C.L., F.R.S., ETC, ON 



something in its place which would have given us a more clear 

 and adequate idea of the causes which brought about this remark- 

 able epoch in the earth's history which immediately preceded, or 

 was partly contemporaneous with, the appearance of man. The 

 Author, however, has not done so, as he may have considered that 

 this wasnot within the scope of his Essay. He endeavours to showthat 

 the Earth-movement hypothesis is untenable, but he does not give 

 us anything in its place. The very distinguished physicist and 

 astronomer, Sir Robert Ball, has within recent times given us from 

 his (an astronomical) point of view, an hypothesis to account for 

 this remarkable period, and, I supposed or hoped, that perhaps 

 Professor Geikie would have discussed Sir Robert Ball's hypothesis. 

 Again, we also know that there is Croll's hypothesis, alsc of an 

 astronomical character, and as Dr. Croll was a fellow T -countryman 

 of Professor Geikie's, I had also supposed that he was prepared 

 either to maintain or to argue against Dr. Croll's hypothesis. 

 Under these circumstances I shall not, on the present occasion, 

 attempt to offer to the Institute any hypothesis : it is not my 

 province to do so, but I would point out one or two arguments 

 in defence of the Earth-movement hypothesis. 



I do not understand why it is that the Author supposes 3,000 

 feet as the necessary elevation of the earth's surface. He says, in 

 order to bring about the glacial condition of the Great Ice Age, it 

 was necessary that the Northern hemisphere should have been 

 elevated 3,000 feet. It seems to me that this is carrying your 

 demand for elevation very much beyond what is at all necessary. 

 For my part, I think it could be very easily shown that an eleva- 

 tion of 1,000 feet would probably cause such a change in the climatic 

 conditions of the Northern hemisphere that a very large amount of 

 glaciation would take place amongst the mountainous regions of 

 Europe and the British Islands, which would also have a very 

 material effect on the climate of the adjoining lands to the south- 

 ward. I do not see, therefore, that it is necessary to demand such 

 an enormous general elevation as that of 3,000 feet. 



Then, as to the movement of the earth's crust. We have in the 

 British Islands the most clear evidence that the inter-glacial epoch, 

 of which Professor Geikie speaks, was contemporaneous with a 

 depression of the land surface, amounting to at least 1,300 feet, 

 because beds of sand and gravel with marine shells have been 

 found, both on the mountains of Ireland and of North Wales, at 



