137 



Miies^and^ The first or outer range of the Rocky moun- 



tains stands out prominently on the western 

 side of Brule lake, and the structure there dis- 

 played is that of an overthrust block of Devonian 

 limestone superposed on Lower Cretaceous. 



ROCKY MOUNTAINS. 



The fault block system of mountain building observed in 

 the southern sections of the Rocky mountains is modified 

 in this section by the substitution of sharp folding for minor 

 faulting, and the blocks between the major faults show 

 complex folds in the beds and are much wider. Two large 

 blocks, whose elevated eastern edges form Roche Miette 

 and Bulrush mouncain, exhibit this folding, while the valley 

 depression between the two is underlain by Lower Cre- 

 taceous rocks containing coal. Mines are being established 

 on both sides of the valley. The lowest rocks outcropping 

 here are of Cambrian age and underlie a series of sediments 

 capped by fossiliferous Devonian limestone, which is 

 exposed in the cliff of Roche Miette. The Cambrian 

 rocks are disposed in a yellow band near the faalL line which 

 separates the lower rocks from the Cretaceous. The 

 succeeding fault blocks are tilted, but not folded, and in 

 that respect resemble the mountains to the south. 



The structural section of the mountains on the Athabaska 

 shows a modification in the outer ranges of the fault 

 block system exhibited on the southern passes. The 

 outer blocks have been deformed by sharp folds, which 

 when traced southward develop into faults, and separate 

 the block into several smaller blocks. Two of the blocks 

 showing this contortion are seen from Pocahontas station. 

 The eastern one of these has its uplifted edge fronting to the 

 east on Brule lake: the second forms Roche Miette, the 

 depressed edge being beneath the valley of Rocky and 

 Stony rivers. Cretaceous beds are found at the back of 

 the first block; some of these beds may also remain on 

 the second, but they are masked by the great deposit of 

 detrital matter in the two valleys mentioned. 



The rocks forming these blocks include a series of sedi- 

 ments ranging in age from Lower Cretaceous downward to 

 Upper Cambrian, all in apparent conformity. The lowest 

 sediments are at the base of the second block. The 

 character of these beds is outlined below : — • 



