16 



University of California Publications. 



[Geology 



thousand feet. This is a surprisingly small amount of rotation, 

 and the attitude of the lava might easily be mistaken for hori- 

 zontal. However, it has been considered that the separated 

 basalt sheets of the Great Basin were never connected. 1 A few 

 basic dykes were found within and near the areas of Pis. 1 and 

 2, and it may be possible to trace the basalt to them. The char- 

 acter of the material is such that a very narrow fissure might 

 discharge considerable molten rock, since the basicity of the 

 rock indicates a great degree of fluidity at a comparatively low 

 temperature. While the latter hypothesis attempts to account 

 for their isolation, it remains to be seen how to account for their 

 attitude. This is one of the 'questions that arose that was not 

 answered beyond the attempt indicated. The author's opportu- 

 nity did not permit of his making any further investigation. 



EXPLORATIONS BEYOND THE REGION MAPPED. 



It was the writer's opportunity to make an excursion to the 

 West Walker and through Carson Valley. This gave him an 

 occasion to make some observations of a general character. The 

 structure of the first system was found to prevail, with now and 

 then suggestions of the transverse system. The West Walker 

 flows through two valleys before it reaches the Main Walker. In 

 flowing through the first of these (Antelope Valley) it bears 

 along near the eastern base of the mountains at the west for a 

 considerable distance, and at the northern end of the valley the 

 course is northeast, passing through the Pine Nut Range, which 

 is very low at that point, there being a considerable mass imme- 

 diately north. The river then turn sharply to the north and 

 swings eastward across the valley, being entrenched on a flood- 

 plain between two bluffs of sandstone. These bluffs are the beds 

 of sandstone that were referred to as of uncertain age when the 

 unconformity of the Tertiary and Quaternary was considered. 

 The bluffs converge toward the east, and the river is more and 

 more confined between them. The stream runs near the base of 

 the northern bluff, and is gradually invading it, thus gradually 

 taking a more and more northward direction, which seems to 

 indicate a tendency of the river to change its course and flow 



1 Mr. G. K. Gilbert, Surveys West of the Hundredth Meridian, Vol. Ill, 

 p. 125. 



