darton: peculiar fault in new mexico 



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Some of the details of the relations are obscured by talus, but 

 many of the features are clearly exposed, especially the contacts 

 of the included sliver of granite. The latter is red, coarse- 

 grained, and massive, of the sort which constitutes a large part 

 of the range, and while it is greatly broken and crushed it shows 

 no fining of grain such as occurs at igneous contacts. The lime- 

 stone near the contact is not in the least metamorphosed. It is 

 shattered and brecciated and for a foot or more includes small 

 angular fragments of granite of various sizes, mingled with broken 

 fragments of limestone as if the two materials had been rolled 

 together along many subordinate fault planes. The precise 



Fig. 1. A, section showing relations 

 of granite to limestone at southeast end 

 of Florida Mountain, 2 miles south of 

 Gym Peak, southeast of Deming, New fj 

 Mexico, looking east; L, limestone; Gr, 

 granite. B, sliver of granite from same 

 (larger scale). 



mechanism of the faulting of the included granite sliver cannot 

 be fully ascertained, for erosion has severed the connection on 

 the outcrop side and the mass extends into the ridge on the 

 other side. It is evident, however, that the granite is a wedge- 

 shaped mass between two principal fault planes with many 

 minor ones, along which it was carried forward into the lime- 

 stone. The latter is one of several large, wedge-shaped bodies 

 overthrust onto the gi'anite by fault planes of low inclination. 

 These faults are similar to one crossing the range a mile north 

 but with planes nearer the horizontal so that erosion has re- 

 moved much of the block, leaving only a few outlying masses 

 of limestone to indicate the nature of the overthrust. 



