674 REVIEWS 



has now passed beyond the preliminary stage. Important results have 

 already been obtained and much more may be expected in the future, espe- 

 cially since the occupation of new quarters by the laboratory will make 

 possible the investigations of mineral behavior under high pressures origi- 

 nally contemplated. The study of the feldspars and other minerals 

 resulted in the location of several cases of reversible changes and one of 

 irreversible change. Wollastonite possesses one crystal form below 1,200° 

 and another above that temperature and either of these forms may be 

 changed to the other. Three forms of magnesium metasilicate may be 

 changed into a fourth by heating, but the reverse change does not occur; 

 and yet enstatite, the magnesium silicate compound common in rocks, is 

 not this stable form. Quartz was found to change over to tridymite at 

 800°, if given time enough ; showing that this mineral, so common in nature, 

 has been formed at a relatively low temperature. *' Quartz-glass," a most 

 useful material which can be raised to a white heat without melting and 

 subjected to sudden changes of temperature without breaking, was success- 

 fully prepared, though quite high temperatures (above 1,600° C.) and some 

 pressure were necessary. The valuable properties of Portland cement 

 have been attributed to tricalcic silicate, but this compound was found not 

 to exist ; further study may reveal the true chemical relations which deter- 

 mine the action of this cement. Textures similar to those of certain schis- 

 tose metamorphic rocks were produced in the laboratory by submitting 

 crystallizing substances to unequal stresses; thus confirming the conclusions 

 of Van Hise in regard to the cause of schistosity in rocks. The published 

 work of the laboratory has appeared in various scientific journals, as 



enumerated in the paper. 



H. H. 



The Mountains of Southernmost Africa. By W. M. Davis. Reprinted 

 from Bulletin of the American Geographical Society, Vol. 

 XXXVIII, October, 1906. 

 One of the best-defined physiographic features of South Africa is the 

 mountain system, occupying the southern border and here referred to as 

 the Cape Colony ranges. It comprises a number of nearly parallel east 

 and west ridges and longitudinal valleys which do not conform in direction 

 to the trend of the southern sea coast but are cut irregularly by it. The sea 

 has advanced on these mountains, leaving but a remnant of the whole sys- 

 tem, and this remnant has itself suffered extensive denudation. Americans 

 will be particularly interested to learn that the Cape Colony ranges are in 

 many respects similar to the AUeghenies. The strata, with the exception 



