408 Annals of the Carnegie Museum. 



between the Jefferson Valley on the east and the Big Hole Valley on 

 the west. 



The relief of these areas varies from hills projecting above the 

 Tertiary deposits, through low, variously-shaped foot hills and ridges, 

 higher hills, and low mountains, to peaks, which, like Gallatin Peak, 

 attain an altitude of ten thousand feet or more. 



The rocks of this formation are, as a rule, fairly well covered with 

 vegetation, sometimes with heavy forests. In some places the dip is 

 quite regular and the stratification plain. This is especially the case 

 along Alder Creek on the western slope of the Tobacco Root Range. 

 In other places there is much contortion and the stratification is not 

 so evident. 



As determined in the field, without careful classification, the rocks 

 would be denominated as quartzyte schists, metamorphic quartzytes, 

 mica schists, hornblende schists, chlorite schists, micaceous gneiss, 

 granitoid gneiss, garnetiferous gneiss, etc. 



The rocks contain many veins of nearly pure quartz and some 

 valuable metalliferous deposits. In the early days of mining in 

 Montana the quartz mines were principally in Archaean rock. At 

 present nearly all the evidence indicates that the vast amount of placer 

 gold which has been taken from Alder Gulch came from near the 

 contact between the Archaean and Cambrian, probably from the upper 

 part of the Archaean, at the foot of Old Baldy Mountain at the head 

 of Alder Creek. 



On Camp Creek east of Melrose there is an excellent section of the 

 Palaeozoic rocks overlying the Archcean gneiss. Their relations are 

 shown in the sketch of the section of this region, made in traveling 

 up Camj) Creek in going from Melrose to Rochester. Though, as 

 stated in my notes which I quote later, I did not carefully examine 

 the exact line of contact between the Archaean and Palaeozoic, I did 

 ascertain that rock which is apjiarently Cambrian cpiartzite is very 

 close to if not in actual contact with the gneiss. 



THE ALGONKIAN? 

 In several localities in the Cordilleran region of Montana there are 

 beds different from the gneisses described above, and lying beneath 

 rocks which contain undoubted Cambrian fossils. They present a 

 problem which will require much work for its solution, and which in the 

 present state of our knowledge is quite puzzling. 1 have ascertained 



