DOUCLASS : GeOI.OGV ok SOUI'HWESIERX MoX TANA. 40!) 



that some of these beds, the ones containing the crystalline lime- 

 stone, overlie the Archrean gneiss in the Ruby Mountains. In some 

 places they are entirely absent and the Cambrian rests on the gneiss. 



The relations of the Arch;\;an, doubtfully Algonkian, undoubted 

 Algonkian, and Cambrian I will tliscuss more fully later. 



The Cherry Ckekk Fdrmaiion. 



Some beds of metamorphic rock near the eastern base of the 

 Tobacco Root Range in the Uj^per Madison Valley southeast of Old 

 Baldy Mountain, and on the opposite side of the Madison River at 

 the western base of the Madison Mountains were named by A. C. 

 Peale "The ('herry Creek Beds," and were assigned to the Algon- 

 kian. They were described as, "a series of marbles or crystalline 

 limestones, and interlaminated mica-schists, i^uartzytes, and gneisses." 

 They were undoubtedly named from Cherry Creek which flows through 

 the exposure. 



Only eight or ten miles distant from the typical locality at the foot 

 of Old Baldy Mountain, what are undoubtedly Cambrian (Flathead) 

 quartzytes rest directly on Archsan gneiss. Below this Alder Creek 

 cuts through a thick series of gneisses and schists. In this series 

 I have never seen the thick beds of crystalline limestones, though I 

 have many times observed the outcrops along the whole length of 

 Alder Creek ; nor does Peale designate them on the map of this region. 

 But they may have been weathered more than the gneisses and become 

 covered with soil and vegetation, thus escaping notice. They appear 

 again, however, in the Ruby Canon west of Old Baldy. I observed 

 several years ago what I took to be a limestone vein in the gneiss in 

 the hills south of Alder Creek. 



Westward and northwestward of the exposure of the limestones in 

 the Ruby Canon they occur on the eastern slope of the Ruby Moun- 

 tains. Here in beds lower in altitude, in a sandy stratum, I found a 

 trilobite, which was determined by S. A. ^HWqv d& Asaphisciis 7C'/ice/eri. 

 This sandstone contained green grains, which appear to be glauconite. 

 Geologically the beds are undoubtedly higher than the crystalline 

 limestones, but time was not taken here to settle the stratigraphical 

 relations. 



l-5ut fiirther to the north in the highest portion of the Ruby Moun- 

 tains I found along the highest ridges a section, showing the relation of 

 the crvstalline limestones to the gneiss, and of this to the Cambrian. 



