REVIEWS lOI 



A Contribution to the Geology of the Leucite Hills, Wyoming. By 

 J. F. Kemp, New York, and W. C. Knight, Laramie, Wyo. 



The Mechanics of Igneous bitriision. By R. A. Daly, Ottawa, 

 Canada. 



The more important facts of the writer's summary are: 



1. The facts of the field. — {a) Lack of sympathy between structural 

 planes in the invaded formation and form of intrusive body, {h) Respec- 

 tive magmatic chambers are not prepared for intrusion by circumferen- 

 tial faulting, (c) Contact phenomena demonstrate some kind of active 

 assimilation of their corresponding country rocks by the respective 

 magmas, {d) In the normal stock there is a lack of any enrichment 

 of the endomorphic zone by the invaded formation ; general freedom 

 in the interior and characteristic abundance of angular inclosures near 

 the contacts ; exceedingly sharp lines of contact with country rock ; a 

 high degree of homogeneity in the igneous body, and common occur- 

 rence of many long and narrow apophyses form the igneous body. 

 {e) Isolated observations prove that solid rocks may sink in molten 

 magmas because of differential density. 



2. The facts of experimental research. — The experiments of Barus, 

 Doelter, Daubree, Cossa, Bischof, Cotling, Morozewicz and others 

 show : (a) that representative natuiral or artificial silicate mixtures, at 

 ordinary atmospheric pressure, become thinly molten at a temperature 

 only slightly above that of solidification ; {f) that, in every instance, a 

 great increase of volume characterizes the change from the solid to the 

 liquid state; (^) that, with strong probability, the volume increment 

 and resulting density decrement are so far preserved in rock mag- 

 mas under plutonic conditions as to forbid the flotation of blocks of 

 the average country rock immersed in the average magma in depth ; 

 {d) that the chief rock-forming minerals are soluble in all of the mel- 

 ted silicate mixtures yet investigated and at the temperature ruling 

 when those mixtures are thinly molten ; (^) that rock magmas become 

 thinly molten at temperatures very slightly above the melting 

 point. 



3. The tests of the hypotheses of overhead s toping and enlargement of 

 magma chambers. — Reasons are given for concluding that the cause cited 

 for overhead stoping is quantitatively sufficient for the majority of stocks 

 and " batholiths," and the detailed phenomena associated with these 

 inclusions are facts of nature expected on the hypothesis. 



