323 



putud, yet it would require the most direct evidence to counter- 

 balance the probability that the shorter path traversed by the sun's 

 rays in summer would have the greater effect in deterniining their 

 intensity. He considers the chief cause of the apparent anomaly 

 to be, that the presence of the snow (to which Dr Richardson point- 

 edly alludes), is mechanically effective in reflecting the solar light 

 upon the sentient thermometer. 



2. An attempt to reconcile the Theories of the Debacle and 

 the Action of Glaciers, in accounting for the Distribution 

 of Erratic Blocks. By Sir G. S. Mackenzie, Bart. 



The author commenced by alluding to the disposition of geo- 

 logists to draw conclusions of a general nature too hastily from the 

 facts observed by them, illustrating this remark by refen-ing to the 

 various opinions successively promulgated, not only by geologists 

 generally, but even by the same geological writer, on the subject 

 of the till or boulder clay, the gravel, and sand, by which Great 

 Britain is every where more or less covered. At one period, all 

 these superficial deposits were referred to the action of water alone ; 

 now it is the fashion to explain them by the agency of glaciers. 



In treating of the appearances presented by these deposits, the 

 author observes, that those which at first sight might be thought 

 to indicate tranquil deposition from water, might in reality be due 

 to a different cause. There is sometimes the semblance of stratifi- 

 cation, which arises from an intci'nal movement and segregation 

 of the different matters in the mass. As a proof that this phe- 

 nomenon does often occur, the author mentioned that, in the old 

 ramparts of Tours formed originally of rubbish, he observed that 

 in a part where they were cut across to form a road, the materials 

 had so arranged themselves as to exhibit stratified beds. 



The author does not offer any positive opinion as to the truth 

 of the theory, which implies that the above-mentioned superficial 

 deposits are due to the ei'osion and movement of glaciers covering 

 the whole surface of the country. He mentions, however, one lo- 

 cality in Ross-shire, where there are appearances on the lateral 

 rocks of a valley strongly indicative of glacial erosion. 



On the supposition that there are phenomena which indicate 

 the action of water as well as of ice, in the formation of these su- 

 perficial deposits, the author states the view which occurred to him, 

 for embracing both of these agents, to be as follows : — He supposes 

 that a volcanic eruption took place in the Icy Sea, some where to 

 the north-west of the British Islands, which had the effect ofbrcak- 



