190 GEOLOGICAL SURVEY OF THE TERRITORIES. 



occurring at many localities, although not covering so extensive an area 

 as the preceding one, consists of orthoclase, mica, and quartz. It is fine- 

 grained, and has, on account of a comparatively large quantity of mica, 

 a dark color. The orthoclase crystals are colorless, transparent, very 

 intimately associated with the quartz and mica. This latter is dark-brown 

 to black, showing single crystals. Quartz is white to colorless, some- 

 times grayish. In consequence of the compact texture, this rock 

 successfully resists decomposing influences, and, wherever found, stands 

 out more prominently than the one before described, c. A third variety 

 differs from the two preceding in appearance as well as in quantitative 

 composition. Orthoclase, quartz, and mica form the crystalline aggre- 

 gate. The orthoclase is pink, translucent, occurring in very small par- 

 ticles, and is by far predominating in quantity. Quartz is colorless to 

 gray, and the mica black, occurring very sparingly. In consequence of 

 the fact that orthoclase forms the main bulk of the rock, it has a pink 

 color, and looks in reality more like a. crystalline mineral than like a 

 compound of separate minerals. With reference to its position to the 

 two varieties described above, it may be said that it occurs in bands 

 or strata within the first one. Had it been feasible, it would have been 

 extremely interesting and important to study the relations that these 

 distinct varieties bear to each other, and to determine whether their 

 relative position is constant under the same relative conditions. 



A phenomenon of some interest was observed a short distance west- 

 ward of station 22. Some of the trachytes, belonging to Nos. 2 and 3, 

 have flown toward the Quartzites, but it appears that the latter may 

 have been too high for them at the time, and they were not reached. 

 At the point indicated, a very large mass of the volcanic material has 

 fallen down perpendicularly for a distance of about 700 feet. This 

 shows that at one time a cave must have existed there, as the possibil- 

 ity of the place having been underwashed is excluded by orographical 

 features as well as by the physical character of the underlying rock. 

 It has frequently been noticed, that at the junction of non-volcanic and 

 volcanic rocks, caves were formed, and it seems probable that we have 

 in this case an analogous occurrence of very considerable extent. 



Besides this continuous granitic area there are the isolated points 

 mentioned above. Near station 7, the granite is coarse-grained, with 

 orthoclase only, readily decomposing. Near Lake Fork, opposite sta- 

 tion 12, and at Handle's Peak it is very coarse, with large crystals of 

 orthoclase and white oligoclase. On the ridge near station 21 it is of 

 the same character, with a large percentage of black mica, giving it 

 upon first sight the appearance of syenite. At all these localities it is 

 exposed for a short distance only, being covered by the overlying 

 trachytes. The irregularity in the elevation of these outcrops points 

 to the fact that either the volcanic disturbances must have had a very 

 marked effect upon the material the lava penetrated, or that prior to 

 them already the configuration of the country was a much varied one. 



I am more inclined to the latter view, from the fact mainly that we 

 find such a very considerable thickness of the volcanic strata at numer- 

 ous places, while at others, although the difference in absolute elevation 

 would not warrant it, this thickness dwindles down to a merely nominal 

 figure compared with the former. 



A question of considerable interest, and at the same time one that I 

 believe can be satisfactorily answered, is that touching the origin of 

 this metamorphic group. Along the northern and eastern borders of 

 the area covered by the rocks of this series, no evidence was obtained 

 that would furnish a satisfactory clew to the answer. On the north- 

 western and southern edges, however, several points were found that 



