abstracts: geology 181 



jection, and the mode of operation is believed to have been essentially 

 the same. 



Certain features which were observed in the gneisses imply properties 

 of the magma which at first sight do not appear mutually consistent. 

 Thus the degree of viscosity imphed by the presence of thinly tabular 

 sheets of inclusions within the granite, standing nearly upright and un- 

 supported except by the magma on either side, does not harmonize 

 with the facility with which magmatic material has been transfused into 

 the original rock. In trying to reconcile these features inquiry has been 

 directed toward a consideration of certain of the physical and chemical 

 properties of magmatic solutions. The question of the critical tempera- 

 tures of volatile substances is discussed in its bearing upon their condi- 

 tion within the magma. Further, the question of the possibility of a 

 viscous magma penetrating the pores of the wall-rock is considered and 

 the problem of a possible differentiation of a magma when injected be- 

 tween the layers of a rock in a multitude of adjacent streams is taken 

 up. Certain inferences are drawn regarding the operation of such pro- 

 cesses and the conclusion is reached that under such conditions of in- 

 jection as prevailed at this locality, the advance of the main body of 

 magma would be preceded by that of a more dilute portion, which would 

 be able to impregnate the wall-rock with facility and initiate processes 

 of transformation and solution which the more concentrated body fol- 

 lowing would carry farther toward completion. C. N. F. 



GEOLOGY. — The Shmumo Quadrangle, Grand Canyon District, Arizona. 

 L. F. Noble. U. S. Geological Survey Bulletin No. 549. Pp. 

 100. 1914. 



The Shinumo quadrangle lies in the western part of Kaibab division 

 of Grand Canyon, Arizona. Geological formations that outcrop are 

 exposed in cross-section in walls of the mile deep canyon. They are, 

 in age: Archean, Algonkian, Cambrian, Devonian, and Carboniferous. 

 The Archean and Algonkian, and the Algonkian and Cambrian are 

 separated by profound angular unconformities of erosion. The Cam- 

 brian and Carboniferous are separated by an unconformity of erosion 

 without unconformity of dip. Devonian strata are present only here 

 and there; they were deposited in shallow depressions in the eroded 

 surface between the Cambrian and Carboniferous. 



The Archean includes the Vishnu schist, made up of gneisses, schists, 

 quartzites, and plutonic intrusive rocks. In the region about the mouth 

 of Shinumo Creek it is a metamorphic complex of quartz, mica, 

 alnd hornblende schists which are invaded by a mass of quartz diorite 



