98 JOSEPH P. IDDINGS 



such diverse nature as gneiss and schist, volcanic tuff breccia and 

 solid lava, limestones, sandstones, and shales. 



The relation of some of these directions of drainage to known 

 fracture planes will be pointed out. The dominant drainage lines 

 in the southern three-quarters of the quadrangle trend about 

 northeast-southwest and northwest-southeast, more nearly N. 

 30'^ E. and W. 30° N., the angle between them being approxi- 

 mately 90°. There are other systems of almost rectangular lines 

 somewhat differently oriented, namely, north-south and east-west. 

 These are well developed in the central eastern part of the quad- 

 rangle. 



Let us consider these systems in some detail, commencing 

 with the main drainage channel, that of the Yellowstone River. 

 This enters the quadrangle on the south in a curiously zigzag 

 channel, known as the Third Canyon, cut in crystalline schists. 

 The longer zigzag lines run northwest, and the shorter are almost 

 at right angles. The northwest direction is followed from Gar- 

 diner to Reese Creek in Cretaceous strata, is exchanged for a 

 more northerly direction as far as Yankee Jim, where the north- 

 west direction is followed through a narrow gorge into the open 

 valley, where a right-angled turn is made to the northeast. From 

 Reese Creek to the open valley the river traverses crystalline 

 schists. 



The dominant northwest line of the river just described is 

 parallel to the most profound fault within the region ; namely, 

 that which threw the whole sedimentary series, including the 

 Laramie Coal Measures, down below horizons of crystalline 

 schists. It is a fault of more than 11,000 feet and probably is 

 more than 16,000 feet. This fault appears to end abruptly at 

 Cinnabar Creek, the principal throw being southeast of Reese 

 Creek. 



It is interesting to observe that the Yellowstone River in no 

 place exactly follows the fault line as it is located on the present 

 surface. But it is evident from the topography of the country 

 south of the river and east of Gardiner that parallel fractures 

 must exist on both sides of the fault line, and these must control 

 the northwest direction of the tributary streams and the longer 



