26 University of California Publications in Geology [Vol. 10 



coincident with intrusion, or subsequent to the solidification of a 

 magma shell? Does the magma supply silica, alumina and iron for 

 the lime silicates, or are these concentrated from the invaded rocks 

 either by a reduction in volume or by meteoric waters approaching 

 the contact? Is the attack of meteoric waters on the solidified but 

 still hot intrusive an important factor? Does the metasomatism proceed 

 by constant volumes? Do the lime-silicates and sulphides develop 

 simultaneously and have they a common source? These are the prin- 

 cipal questions now under discussion. Each of them seems to have 

 been answered satisfactorily for individual deposits, but the problem 

 remains how far one pattern may fit the many known occurrences, and 

 what factors determine diversities within the type. 



Any adequate conception of the genesis of contact deposits must 

 be based on the constant relationships which they exhibit, but must 

 be sufficiently elastic to allow for observed diversities. Thus, to add 

 either descriptions of peculiar features of individual deposits, or to 

 point out relationships so often recurring as to be scarcely fortuitous, 

 is to make a contribution to our knowledge of the subject, even if the 

 genetic significance be not fully comprehended or be incorrectly 

 stated. 



Statement of Thesis 



This paper is an endeavor to point out a common, perhaps a 

 general, spacial relationship between ore and garnet zones in the con- 

 tact deposits of the North American Cordillera. It is certain that in 

 many deposits the ore bodies favor the limestone rather than the 

 intrusive side of the garnet zone. In several places the ore comes 

 directly up to the igneous contact, but so far as is known to the writer 

 no clear occurrence has been described where barren lime-silicate rock 

 continues outward far beyond such ore. In the case of engulfed blocks 

 of limestone which have suffered metamorphism the limestone side 

 of the garnet mass is toward the central part of the block, and here 

 ore is found in several localities. In some of these cases all of the 

 limestone has disappeared but the ore is centrally situated. 



In the following paragraphs this relationship is pointed out in 

 brief descriptions of several contact deposits, and finally its bearing 

 upon modern theories is suggested. 



Examples 



Washington Camp, Arizona. — The ore deposits at Washington 

 Camp occur locally on the border of a great island-like mass of lime- 



