REPORT OF MEETINGS FOR 1903 257 



Probably the Cretaceous rocks formed the surface strata. It 

 was through these that the rivers slowly cut their way down 

 to a lower level, until they came upon strata of different 

 kinds. At this juncture some curious and perplexing changes 

 in the physical geography of the district took place. In 

 many cases the courses of the rivers were gradually changed, 

 or their channels were modified in many difiPerent ways. It 

 is as far back as 1881 that I gave a detailed account of the 

 changes, induced by the varying degrees of destructibility of 

 the strata, that the River Eden, in the north of England, 

 underwent in consequence of meeting with similar conditions. 

 I have some reason to think that the paper in question was 

 the first in which the importance of these factors was pointed 

 out. 



The valleys had been shaped, into very much their present 

 form, and the general aspect of the country was much as 

 it is now at the period (very far back in the past if we measure 

 by the ordinary chronological standards) when the Age of 

 Snow set in. The details of the waxing and waning of that 

 remarkable set of events cannot be given here, even if they 

 were needed. Suffice it for the present purpose to say that 

 the land at the commencement of the Age of Snow stood 

 much higher above the sea level than it does now. This 

 was one of the reasons why it snowed in those days where 

 it would rain now. The snow did not flow off the surface, 

 as rain water does, but continued to accumulate until it 

 began to find its way seaward in the form of moving masses 

 of land ice. These, in time, increased in volume until they 

 eventually attained in many parts of Scotland to a thickness 

 of two or three thousand feet. Seeing that each thousand 

 feet of thickness of such material presses upon each square 

 foot of the rocky bed with a weight of over 25 tons ; and 

 seeing, further, that the ice was heavily charged in its lower 

 parts with stones, mud, and sand, and that the period during 

 which these conditions endured was, at the least, one of several 

 hundred thousand years — one c.an hardly wonder that important 

 modifications of the old surface features were brought about 

 by these glacial conditions. As a matter of fact, most of the 

 river valleys were both deepened and widened by the prolonged 

 grinding by the ice ; and the erosion effected in this way wag 



