EFFECT OF HIGH PRESSURES 675 



factorily the whole of the experimental work hitherto done, conflicts with none 

 of the available direct evidence. 



It follows, therefore, that we can determine the effect of pressure on a solid 

 system only if we can define the character of the compression (with reference 

 to its approach to uniformity or otherwise) as well as its magnitude, and even 

 then only when the requisite thermal and other data characteristic of the 

 system are available. 



Discussion 



Prof. H. F. Reid : Prof. James Thomson explained the flow of glacier ice as 

 the result of melting and regelation. This theory was accepted for a time, but 

 latterly glacialists have inclined toward the idea of ordinary plastic flow of 

 glacier ice. Must we now go back to Thomson's theory as the explanation of 

 plastic flow? When a copper wire is bent do we have melting of the particles 

 of the wire? This is a new conception of plasticity. 



Dr. A. L. Day : The theory is not entirely new, but this is, so far as I know, 

 the first attempt to extend it to cover such a wide range of phenomena and to 

 differentiate definitely between the effects of uniform (hydrostatic) and non- 

 uniform compression. 



STRUCTURAL FEATURES OF A PORTION OF SOUTHEAST IDAHO 

 BY R. W. BICHAEDS AND G. B. MANSFIELD 



(Abstract) 



For the past four years the United States Geological Survey has carried on 

 detailed geologic work in southeast Idaho for the purpose of securing data for 

 classifying public lands supposed to contain deposits of phosphate. The phos- 

 phate occurs in rocks assigned to the Permian, and is accompanied by a rather 

 full series of Paleozoic and Mesozoic rocks. The whole sedimentary series is 

 thrown into pitching folds, with trend curving from nearly north-south to 

 northwest. The larger folds are relatively simple, but about their margins 

 there are frequently faults and subordinate folds that make the structure com- 

 plex. The folded region is traversed by a great thrust fault, the Bannock 

 thrust, with warped plane and irregular trace. 



BANNOCK THRUST— A MAJOR FAULT IN SOUTHEAST IDAHO 

 BY B. W. BICHAEDS AND G. B. MANSFIELD 



(Abstract) 



The work of members of the United States Geological Survey in the phos- 

 phate reserve of southeast Idaho during the years 1909-1911 has led to the 

 recognition of an overthrust fault that appears to have unusual extent and 

 magnitude. 



Several faults at first supposed to be independent are now interpreted as 

 parts of a single great thrust, the plane of which has been warped and partly 

 unroofed by erosion. This great fault has been called the Bannock thrust 

 from Bannock County, Idaho, where it is well displayed. 



Rocks of Cambrian to Mississippian ago have been thrust on Triassic to 



