258 REVIEWS 



The pyrargyrite and proustite of the ores were apparently deposited after 

 the primary ore had been somewhat fractured. They were not observed 

 intergrown contemporaneously with any of the undoubtedly primary ore min- 

 erals. In view of this fact and their apparent playing out with depth, they 

 are regarded as products of downward enrichment. 



To the reviewer, it seems that this sort of evidence is rather unsatis- 

 factory as a guide in developing a mine, since the same distribution and 

 lack of intergrowth of the two silver minerals might well be attributed 

 to their irregular deposition from late hypogene solutions. 



But such minor points are almost negligible. The paper is well 



illustrated with camera lucida drawings. It is a very real contribution 



to applied economic geology, and it is to be hoped that the writer will 



continue with his fruitful studies of silver enrichment. 



Charles H. Behre, Jr. 

 Lehigh University 



Geologie von Mexiko. By Wilhelm Freudenburg. Gebriider 



Borntraeger, Berlin, 1921. Pp. viii+232, pis. 2, figs. 29, 



tables. 



' This publication is a digest of the existing literature on Mexican 



geology and as such it fills a distinct need. Under section i, "Summary 



of Morphology," the author treats of boundaries, coasts, areal extent, 



orographic elements, vulcanism, and faulting. He then describes in 



turn the seven physiographic provinces of Mexico and their history, 



following Warren N. Thayer. 



Section 2, which is headed "Stratigraphy and Kinds of Mountains," 

 constitutes nearly half of the volume. Begirming with the Archean, 

 the formations are given brief descriptions and the geologic history inter- 

 preted as far^s possible from existing knowledge. Considerable promi- 

 nence is given to the Mesozoic, particularly the Jurassic and Cretaceous. 

 Typical Mexican stratigraphic successions (including also the fossils) are 

 correlated with the European time scale in several diagrammatic sections. 



The subject of vulcanism fills most of the remainder of the volume. 

 It is noteworthy that while Tertiary and Quaternary effusives surface 

 a considerable fraction of the whole area of Mexico, the post-Cambrian 

 intrusives are comparatively insignificant. "The Active and Extinct 

 Volcanoes of Mexico " ; "Relation of the Tertiary Vulcanism to the Struc- 

 ture"; and "Relations between Volcanoes and Earthquakes" are the 

 subjects of the next three sections, and attest the fact of the great impor- 

 tance of vulcanism in the recent geologic history of Mexico. The mineral 

 deposits of Mexico are given as much space as could be expected in a 



