STRUCTURAL DETAILS 



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 6 i i 



]S^iimbers 10, 11, 12, 13. The relations of four small buttes west of 

 Salazar are of special io^terest. A north-and-south dike (plate 29), 

 from 2 to -1 feet in width, occupies a fault fissure, the evidence of fault- 

 ing appearing where a somewhat massive sandstone meets softer sands 

 and shales at the fissures. At one point the dike suddenly expands into 

 a ])utte some 20 feet in width by ;35 in length, composed of the peculiar 

 agglomerate so often found in the large buttes, and of cohuiuiar basalt, 

 the columns being irregularly curved. A short distance south is a much 

 larger butte, also an expanded portion of the dike, showing beautifully 

 curved basaltic columns more or less radially disposed (plate 29). From 

 this point a branch dike seems to run off to the west, expanding into 

 small buttes at two points. The first of these two buttes is composed in 

 part of the agglomerate containing sandstone fragments, while basaltic 

 columns are approximately horizontal on either side, showing a form 



l'"'io,n!E 10. — IJUtijiiiin shdirinij J.tiiitiini (if lliittc iiiiinhcr JJ/ to siirroiniiUny SeiUme.nta 

 (Shales inijped liij tidJiilstoiie) ami to other Itiittes in the Rer/inii. 



transitional between dike and butte. It is clear that the buttes repre- 

 sent igneous rock Avhich filled tubular conduits leading up throiigh the 

 sediments, just as the associated dike represents igneous rock Avhich 

 filled a fissure in the sediments. 



Number 14 (plate 27, and figure 10). SoutliAvest of Salazar is a 

 butte, 75 or 100 feet in diameter, composed almost entirely of agglom- 

 erate which included large fragments of sandstone and shale. This 

 butte is surrounded by horizontal gray shales capped by yellow sand- 

 stone. On three sides these lieds rise practically to the present summit 

 of the butte, erosion having etched out a semicircular depi'ession about 

 the immediate contact, leaving the butte somewhat isolated from the 

 enclosing sediments. That the contacts about this rudely cylindrical 

 butte must have been vertical is quite evident. The direct contact is 

 occasionally still visible, the beds being bent upward in some places near 

 the butte, but remaining horizontal elsewhere. Sedimentary rocks, well 

 exposed, were traced all around the butte without discovering any indi- 

 cation of a dike. 



