REVIEWS 203 



The fluorite has possibly also some connection with the presence of 

 the telluride, as fluorite is common elsewhere where telluride ores occur. 

 The ore constituents were probably introduced in a liquid form, 

 probably hot and probably hastened by steam and other vapors. The 

 process of deposition was largely one of replacement ; this may have 

 been by chemical action or by deposition in minute cavities after the 

 removal of constituents of the country rock. The latter Dr. Penrose 

 thinks more probable. The deposition was caused principally by 

 chemical reaction with other solutions rather than by reaction with the 

 country rock. 



It is to be regretted that a direct investigation of the problems of 

 the source of the ores and their mode of deposition could not have 

 been made. The study given to the subject is confessed to have been 

 inadequate for final results. Though the conclusions reached by the 

 author seem quite probable, they can be classed only as probabilities 

 pending complete inquiry. 



As a final criticism of this in so many respects valuable and excel- 

 lent report, the cuts or the figures illustrating it might have been 

 improved upon. They are somewhat too diagrammatic and most of 

 them seem to be more of illustrations of the writer's ideas than actual 

 sketches "from life" in the mine. This does not apply to all of the 

 figures, nor to the small mine maps or plates which are inserted. 

 These are excellent and appear to have been carefully compiled from 

 the mine surveys. Arthur Winslow. 



Telluride, Col., 

 January 5, 1897. 



Glacier Bay and its Glaciers. By Harry Fielding Reid. United 

 States Geological Survey, i6th Annual Report, 1894-5. PP- 

 415-461. Plates LXXXVl-XCVI. 

 The studies of Muir glacier conducted by Professor Reid in the 

 summer of 1890, and the results published in the National Geographic 

 Magazine, Vol. IV, were continued and extended in the summer of 

 1892 and the results recorded in the report named above. During the 

 earlier expedition, attention was restricted to Muir glacier and its 

 tributaries, of which an excellent map was published ; the later expe- 

 dition had for its main object the exploration of the western extension 

 of Glacier Bay with its numerous inlets and many glaciers. 



