Revieus — Rocks and their Origins. 379 



pleasantly written throughout ; and the author contrives, in his 

 limited space, to give information not only concerning the latest 

 researches and views, but of the studies of the earlier workers among 

 locks, such as Cordier, Macculloch, Scrope, Ehrenberg, and Sorby. 

 He remarks that "we are still far from discovering the primitive 

 crust formed about a molten globe", and suggests that the "early 

 sediments became frequently immersed in baths of molten matter, 

 and that contact-metamorphism and admixture on a regional scale 

 have produced in them the characters that have been attributed to 

 a fundamental gneiss ". 



"While the Pre-Cambrian and early Cambrian limestones may have 

 been products of chemical precipitation, as they show no signs of 

 organic agency, yet, as Rutley pointed out (1893), the features may 

 be due to metamorphic influence, as in the case of the Carrara 

 Marble. Attention is drawn to altered forms of massive limestone 

 that have become dolomitic or phosphatic, and to the replacement of 

 limestone by silica ; here a few words might have been written on 

 the changes into ironstone. 



In treating of clays the author gives some account of Boulder-clay, 

 Temarking that " Swiss glaciers are now so limited that they are of 

 very little use to us when we seek to explain the origin of boulder- 

 clay " ; and he appeals to the great continental glaciers of polar regions, 

 giving also some personal observations on the minor glacial action in 

 ISpitzbergen. 



The work is intended for those who are not specialists, and we may 

 cordially commend it to junior students and general readers, while at 

 the same time many a teacher will be glad of its helpful guidance. 



V. — Geology and Physics. — The question of the depth of the zone 

 of flow in the earth's crust is discussed by Professor Frank Adams 

 {Journ. Geol , xx, p. 97, 1912). By means of experiments he has 

 come to the conclusions that at ordinary temperatures, but under 

 the conditions of hydrostatic pressure or cubic compression which 

 exist within the earth's crust, granite will sustain a load of nearly 

 100 tons to the square inch; that under the conditions of pressure 

 and temperature believed to obtain within the earth's crust, empty 

 ■cavities may exist in granite to a depth of at least eleven miles ; and 

 that mineral veins and deposits may thus be formed to as great 

 a depth. To the same Journal (p. 119) Mr. L. Y. King contributes 

 an article "On the Limiting Strength of Eocks under conditions of 

 stress existing in the Earth's interior". His experiments show that 

 no state of shearing stress in the crust of the earth, due to the 

 weights of continents and mountains, can cause the collapse of the 

 rock in the neighbourhood of a small cavity. It is also shown that as 

 far as hydrostatic pressure in the earth's crust is concerned, a small 

 cavity at ordinary temperatures will remain open, provided the depth 

 does not exceed a value between 17-2 and 20-9 miles. 



VI. — Canadian Clay and Shale Deposits. — A memoir on The Clay 

 and Shale Deposits of Nova Scotia and portions of Neio Brunswick, 

 by Mr. Heinrich Eies, assisted by Mr. Joseph Keele, has been issued 



