24 James Geikie — On Changes of Climate. 



the beds refen-ed to are of marine origin, many have been deposited 

 in fresh water. I believe my brother was the first to recognize the 

 significance of these beds, although the fact of their occurrence 

 in the Till was previously well known. He showed that the ac- 

 cumulation of the Till must sometimes have been interrupted and 

 certain valleys cleared of ice " up to a height of at least 800 or 900 

 feet above the present level of the sea." Since the publication of his 

 paper on the Scottish Drift,^ inter-Glacial beds have been met with 

 in almost every part of the country ; and from the fact that they 

 occur not only in the Till of the Lowlands but also in that of 

 the deep and narrow valleys of the Southern Uplands, we are 

 warranted in concluding that the warmth of the inter- Glacial 

 periods was sometimes such as to melt off the ice entirely from 

 the Lowlands ; for at a time when streams were flowing in the 

 deep green valleys of the Peeblesshire hills, it is utterly impos- 

 sible that glacier ice could ^ have rested uj)on any portion of the 

 great Central Valley. If glaciers continued to exist in Scotland 

 throughout each inter- Glacial period, they could only have done 

 so in the retired glens of the Highlands and some of the high 

 valleys among the mountains of Galloway. 



The disappearance of a mer de glace, which in the Lowlands of 

 Scotland was probably over 2000 feet in thickness, could only have 

 been effected by a very considerable change of climate. Nor does 

 it seem at all unreasonable to suppose that the comparatively mild 

 and genial periods, of which some of the inter-Glacial beds are 

 memorials, may actually have endured for as long a time as those 

 arctic or glacial conditions which preceded and followed them. 



We shall probably never learn how many great changes of climate 

 took place during the accumulation of the Till and its associated 

 deposits. This arises from the fact, already adverted to, that during 

 every period of intensest cold, when the country was covered with a 

 more or less thick sheet of snow and ice, the loose materials which 

 in the preceding age had gathered in river valleys and in lakes would 

 almost inevitably be subjected to excessive denudation. That the 

 records of mild inter-Glacial periods should be at the best but frag- 

 mentary is no more than one might have expected. The wonder is 

 not that they should be so interrupted, but that any portion what- 

 ever has been spared. And yet in sheltered hollows we find some- 

 times two, sometimes three, and even four beds of Till separated by 

 intervening deposits of gravel, sand, and silt. We cannot assume, 

 however, that only four cold periods and three intervening ages of 

 milder conditions were comprised within the first stage of the great 

 Glacial epoch. For aught that we know there may have been many 

 revolutions of climate. But however that may have been, no one who 

 shall give the matter some thought will doubt that the lapse of time 

 represented by the Scottish Till and its intercalated beds must have 

 greatly exceeded that required for the deposition of the subsequent 

 marine and later glacial drifts. We have a difficulty in conceiving 

 of the length of time implied in the gradual increase of that cold 

 ^ Trans. Glasgow Geol. Soc. vol. i. part ii. 



