Action of Glaciers. 435 



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

 cation, which arises from an internal 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 docs not offer any positive opinion as to the truth 

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

 deposits are due to the erosion 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, tho 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 of break- 

 ing up the ice along the coasts, and that icebergs or sheets of ice 

 loaded with cargoes of boulders, clay, and gravel, were driven or 

 floated over the British Islands, where they dropped their cargoes, 

 and, in many instances, stranded on the hill tops. At this period, 

 the author supposes that the relative levels of land and sea were 

 very different from what they arc at present, a great part of the Bri- 

 tish Islands being then submerged. This theory, the author stated, 

 was not the result of much reflection or observation, and he merely 

 threw it out for the consideration of geologists. 



3. Contributions to Optical Meteorology. No. I. On the Po- 

 larization of the Light of the Sky. By Professor Forbes. 



The author began by recapitulating the observations already made 

 known on this subject. 



The facts generally admitted (principally on the authority of M. 

 Arago) appear to be, (1.) That a clear sky reflects light polarized in 

 planes passing through the sun, the eye of the observer, and the point 

 of tho sky observed. (2.) That this polarization is a maximum in a 

 zone 90° from the sun. (3.) That in the parts of tho sky nearly op- 

 posite to tho sun, this description ceases to be accurato ; for tho po- 

 larization, in a vertical piano passing through the sun and tho ob- 

 server, vanishes at an angle with the sun considerably less than 180°, 

 — perhaps 150° or 100° (varying according to circumstances), — and 



