174 PHYSICAL GEOLOGY. 



a blackish colour usually, and having a vitreous lustre. No explana- 

 tion is attempted. G. A. L. 

 Costa de Bastelica, Michel. Les torrents, lours lois, leurs causes, 

 leurs effets, moyens de les reprimer et de les utiliser. Leur 

 action geologiquo univcrselle. [Torrents, their laws, causes, and 

 effects, the means of checking and utilizing them. Their uni- 

 versal geological action.] 8vo, Paris. 

 Cropt, Eev. C. Some modern aspects of Geological Science. [Abs- 

 tract.] Trans. Plymouth Inst. vol. v. part i. pp. 33, 34. 

 Considers that the sea alone is capable of giving to the earth's surface 

 its main outlines. 



Croll, J. On the Physical Cause of Ocean Currents. Phil. Mag. 



ser. 4, vol. xlvii. pp. 94, 168, 434. 

 These papers have a geological bearing, because, according to Mr. 

 CrolFs views, the climatic conditions of the globe are dependent to an 

 enormous extent on the distribution of heat by ocean-currents. The 

 author believes that, when the eccentricity of the earth's orbit was at 

 its maximum and the northern winter occurred in aphelion, the differ- 

 ence of temperature between the arctic and equatorial regions would 

 be greater than that between the antarctic and equatorial regions ; 

 hence the IST.E. trades would be stronger than the S.E. trades, and 

 much of the warm equatorial water that is now driven, by the action 

 of these and other winds, into the northern hemisphere, would be 

 diverted to the southern hemisphere. Thus one source of heat would 

 be transferred from the north polar to the south polar regions, and the 

 cold already existing in the first would be intensified, while the genial 

 climate of the second would be rendered still more genial. A. H. G. 



. On the South of England Ice-sheet. Geol. Mag. dec. 2, 



vol. i. p. 257. 



Believes that during the last Glacial period the Scandinavian ice- 

 sheet passed from the Baltic over Denmark, into the German Ocean, 

 and that, if this were so, part of it must have passed across the south 

 of England, and entered the Atlantic in the direction of the Bristol 

 Channel. A. H. G. 



. On the Physical Cause of the Submergence and Emergence 



of the Land during the Glacial Epoch. Geol. Mag. dec. 2, vol. i. 

 pp. 306, 346. 



Shows that, in order that a sheet of continental ice may slide, it 

 must be thickest in the centre, and estimates that the Antarctic ice-cap 

 may be 12 miles thick in the middle, giving facts which show his 

 estimate is not excessive. He then shows how the transference of the 

 ice-cap to the other pole would result in a rise of the sea-level, and 

 points out that the rise would be greater if the interior of the earth be 

 fluid than if it be solid to the centre. He applies his views to explain 

 the intermixture of the remains of northern and southern mammals in 

 old river-gravels. A. H. G. 



