Douglass: Geology ok Southwf.si'f.rn Montana. 413 



2. The Cherry Creek Formation, (d) " .\ series of marbles, or crys- 

 talline limestones and interlaminated mica-schists, (juartzytes and 

 gneisses," ^ in the foothills in the region of Cherry Creek in the Ui:>per 

 Madison \'alley. 



Cherry Creek Formation? (/-') A thick body of massive crystalline 

 limestone and a body of a similar thickness of stratified gneiss which 

 lies between Archaean gneiss and the Cambrian shales. This proba- 

 bly is the equivalent of the Cherry Creek formation, but to avoid 

 possible confusion, I will call these for the present the Ruby crystal- 

 line limestone and gneiss. 



3. The Belt Formation, (a) Coarse and fine-grained sandstones, 

 quartzytes, red and green slates and shales, and in the Horsehoe Hills 

 north of the Gallatin valley, containing conglomerates near the base, 

 and higher in the series silicious limestone and argillites. This for- 

 mation occurs in the Horseshoe Hills, in the Belt Mountains, in Smith 

 River Valley and in other places. 



(fi) Reddish quartzytes and slates and green slates and argillites 

 principally in the region of Missoula, Montana. Again to avoid con- 

 fusion I will call these the Missoula quartzytes and slates. 



By referring to the Three Forks Atlas Sheet it will be seen that the 

 Belt beds are in all the localities of their exposures overlain by Cam- 

 brian strata, and in the region north of the Gallatin there is no doubt 

 as to the Cambrian age of these latter rocks. In the Bridger range 

 the relations are the same — that is in the portion represented on this 

 sheet. But on the Livingston sheet it is seen that in the southern 

 part of the Bridger range the Cambrian is in contact with the Archaean. 

 South of this the Belt beds are not seen. 



If we now refer to the Little Belt Atlas Folio we seem to find 

 what we wish, viz.: the relation of the Algonkian to the Archaian. 

 Here on three sides of the town of Neihert the Belt beds are repre- 

 sented as lying between Archeean gneisses and schists below and Cam- 

 brian rocks with Middle Cambrian fossils above. But on page i of 

 this folio Mr. Weed says: "The older rocks of the region are the 

 gneisses and schists found in the Little Belt Range in the northwestern 

 part of the ciuadrangle. They are in part at least of igneous origin. 

 Being a complex of rocks whose relations and origin are uncertain, 

 and forming a group whose characters are alike throughout and differ 

 from all other formations, they are considered to be of Archaean 

 age. ' ' 



* Three Forks Atlas Folio, No. 23. 



