DdUGLASS: GkOLOGV of SOUIHWF.STERN MONTANA. 415 



Ruby Mountains were formed by metamorphisni of the Iklt beds is 

 naturally suggested, but this would not get rid of all the difficulty, 

 for both are api)arently absent from a great part of the area in the 

 regions in which they occur. Gneisses probably underlie all the 

 sedimentary rocks, but the ones containing the crystalline limestones 

 appear at present to be confined to a restricted portion of the Tobacco 

 Root and Ruby Mountain Ranges. Perhaps more careful observa- 

 tion may extend this area. 



Above the old gneisses the first beds that are fairly constant, so far 

 as my observation goes, are quartzytes that are apparently Flathead 

 quartzytes. In some places they surely are. I will not say that these 

 are not sometimes wanting, but they, at least, are widely distributed, 

 as are the shales and limestones above. These latter are said to con- 

 tain Middle Cambrian fossils. 



The idea that after the deposition of Algonkian strata there were 

 continental conditions, with upheavals, faulting, and a vastly long 

 period of erosion, presents itself, but this theory like all others has 

 apparent difficulties as a sufficient explanation of all the data. The 

 truth is in all geological inquiry imagination is apt to run far ahead 

 of observation and it often hinders the accumulation of facts which 

 would help toward the settlement of the problem.* 



PAL.-EOZOIC. 



Dr. A. C. Peale, in his " Palaeozoic Section in the Vicinity of Three 

 Forks, Montana," (Bull, no, U. S. Geol. Surv.), has described the 

 excellent Palceozoic section here. The studies of the various areas 

 mapped by AV. H. Weed, of the United States Geological Survey, and 

 my own observations, show that the upper portion of the Palaeozoic, 

 especially, possesses much local variation in lithological and other 

 characters, and its more thorough study will undoubtedly be inter- 

 esting. 



I give a sketch section made on Camp Creek east of Melrose. 

 With the Three Forks Section there is a general similarity, and 

 though I found fossils only in the Devonian shales, yet the different 

 members of the series can be assigned to their position in the scale 

 with a fair degree of probability. This section is interesting, as only 



♦ ?"or an interesting discussion of the relations of these different formations see " Pre- 

 Cambrian Fossiliferous Formations." C. D. Walcott. Btt//. Geol. Soc. A»ier.,\o\. 

 lo, p]). 210-215. 



