ABSTRACTS 



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GEOLOGY. — Geology of the Navajo country. A reconnaissance of 

 parts of Ariftona, New Mexico, and Utah. Herbert E. Gregory. 

 U. S. Geological Survey Professional Paper 93. Pp. 161, with 

 maps, sections, and illustrations. 1917. 



The region bordering the Colorado canyons between Little Colorado 

 and San Juan rivers and extending southward to the line of the Atchi- 

 son, Topeka & Santa Fe Railway is described. The primary object of 

 the investigations was to "spy out the land," with a view to suggest- 

 ing ways in which the country could be more fully utilized. The 

 region is arid, and the geologic field work was therefore designed chiefly 

 to obtain information concerning the water supply. 



The Navajo country is part of the Colorado Plateau province, a 

 region of folded and faulted sedimentary rocks traversed by innumerable 

 canyons. The consolidated sedimentary rocks exposed in the Navajo 

 country are chiefly of Mesozoic age — -Triassic, Jurassic, and Cretaceous. 

 The predominant rock of the whole Navajo country is sandstone of 

 medium grain; limestone and conglomerate are much less common, and 

 typical clay shale is rare. 



In the Grand Canyon district the dominating structural features are 

 represented topographically by flat-topped plateaus, bordered by lines 

 of displacement trending roughly north. The simplicity of folded 

 structures in the Grand Canyon district is not, however, duplicated in 

 the region east of Colorado River. Synclines and anticlines, both 

 broad and narrow, sharply delineated monoclines, and domical up- 

 warps follow one another in succession or abut against one another 

 like waves in a choppy sea. In one feature only — their general trend — 

 do the flexures displayed in the Navajo country simulate those of the 

 region farther west. Ten major folds and eight minor folds, in addi- 



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