10 DEPARTMENT OF THE INTERIOR 



2 GEORGE V.„ A. 1912 



ter IV. discusses the stratigraphy and structure of the Clarke range (Livings- 

 ton range of Willis), the most easterly of the mountains covered by the survey. 

 Willis' results on the succession of formations were confirmed by detailed study. 

 The oldest formations in this part of the Rocky Mountain system are the Altyn 

 and Waterton niagnesian limestones and dolomites. The former is believed to 

 be considerably thicker than the minimum estimate given by Willis, in whose 

 traverse the lower part of the Altyn formation was not visible. The base of 

 the Waterton formation is concealed. At Waterton lake a boring has located the 

 plane of the Lewis overthrust at a depth of about 1,500 feet below the lake-level. 

 At that level the bit of the machine entered soft shaly rocks assigned to the 

 Cretaceous. 



The fossil Beltina danai was found in the Altyn formation. No other 

 determinable fossils were found in this range, the sediments of which were 

 assigned by Willis to the Belt terrane of the Algonkian. They are here alluded 

 to as the Lewis series. At the Flathead river, a local fresh-water, fossiliferous 

 deposit of clays and sands — the Kishenehn formation — occurs; it is assigned 

 to the Miocene. 



The Clarke range forms a dissected broad syncline, which is accidented 

 with a few faults and secondary warps. The valley of the North Fork of the 

 Flathead river is an eroded graben or fault-trough. The range has been moved 

 eastward at least eight miles along the great Lewis thrust. The writer favours 

 the view that this thrust, as well as nearly all the other deformation represented 

 in the range, dates from the close of the Laramie, but this has not been finally 

 proved. 



Chapter V. — Continuing westward, the older members of the geosynclinal, 

 a 7 l unfossiliferous, were found to make wp the greater part of the MacDonald 

 and Galton ranges. The lithology has, however, changed and in some cases 

 new names are given to the constituent formations. The whole conformable 

 group, corresponding to the Lewis series, is called the Galton series. 



On the east and west sides of the Galton-MacDonald mountain group down- 

 faulted blocks of fossiliferous limestone, upper Devonian to Mississippian in 

 age, make contact with some of the lowest members of the much older Galton 

 series. 



The dominant structural unit of the twin ranges is the fault-block. 



Chapter VI. — West of the Rocky Mountain Trench the geosynclinal rapidly 

 af-sumes a lithological character markedly different from that found in the four 

 ranges just mentioned. The Purcell system is largely composed of massive 

 quartzites and metargillites, forming the Purcell series, which is the more 

 silicious equivalent of the dominantly argillaceous and calcareous or dolomitic 

 sediments of the Lewis and Galton series. The Purcell series is of much more 

 homogeneous composition than the other two series. 



An interbedded volcanic formation, of the fissure-eruption type, has been 

 followed from the Great Plains to the summit of the McGillivray range, where 

 the lava is thickest. It is named the Purcell Lava. A special feature of the 



