i64 REVIEWS 



force analogous to the expansion of water on freezing, which has crowded 

 the rock fragments asunder." 



In 1900 also an article by R. A. Daly appeared in the Journal of Geol- 

 ogy (Vol. VIII, pp. 135-50), in which the author shows the evidence of 

 mechanical force exerted in the formation of calcareous concretions. 



Messrs. Becker and Day have now not only demonstrated the mechani- 

 cal force of growing crystals, but they have been able to measure that 

 force in some instances. The bearing of this work upon the formation of 

 veins is recognized by the authors, for they conclude that 

 it thus becomes possible that .... great veins have actually been widened to 

 an important extent, perhaps as much as 100 per cent., or even more, by pressure 

 due to this cause. .... Again, in a vein where auriferous quartz is being depos- 

 ited, the growth of crystals may readily extend the space in which successive 

 crops of crystals might grow, so that in certain cases .... the deposition of ore 

 might continue almost indefinitely. 



The investigation is to be continued, and we shall be greatly disap- 

 pointed if it does not prove to be one of the most important modern 

 contributions to the theory of vein deposits. 



J. C. Branner. 



