114 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



seen in the more quartzose layers. As a rule these beds, like the main lime- 

 stone, were fetid under the hammer. A strong cleavage affects them, with 

 strike N. 12° W. and dip, 75 — 80° E.; it suggests local faulting parallel to the 

 trend of- the Flathead valley. 



On the slope immediately above the reddish zone the normal gray, massive 

 limestone begins and continues westward to the great fault where the limestone 

 and the MacDonald metargillite make contact. In that traverse the dip 

 gradually steepens to a maximum of about 40° or more, to the south-westward. 

 At the 6,500-foot contour and one-half mile north of the Boundary line, the dip 

 abruptly changes to 55° S.W., with strike N. 55° W. The change of dip takes 

 place at a meridional belt of intense shearing, where, for fifty feet across the 

 belt, the limestone is a white, brecciated marble. East of this shear-belt the 

 fossils collected are Mississippian in age; west of it the fossils are Devonian. 

 The shear-belt seems, thus, to mark the outcrop of a strong fault along which 

 the Mississippian limestone has been dropped down, relatively to the Devonian 

 on the west. 



That traverse is probably typical of a number which might be made across 

 the eastern block. The relations are those of step-faulted blocks with down- 

 throw to the east. Further remarks made on page 117 as to + he local structures 

 should be added to this brief account. Since the distribution and throws of the 

 various faults are unknown, it is not possible to state the true thicknesses of 

 the fossiliferous limestones. Either the Devonian or the Mississippian lime- 

 stone is certainly many hundreds of feet in thickness; their combined thickness 

 must be well over 1,000 feet. 



Neither top nor bottom of the series has been discovered in the Boundary 

 belt. In the Yakinikak valley, about five miles south of the Boundary line, in 

 this same mountain range, Willis found a small mass of limestone carrying 

 numerous fossils of the Saint Louis horizon of the Mississippian. He writes 

 that the limestone — 



' Is without upper stratigraphic limit, but rests conformably on a 

 quartzite, which is unconformable on Algonkian strata. The quartzite 

 is about 25 feet thick, and it and the limestone lie in a nearly horizontal 

 position. The name Yakinikak is here applied to the limestone, exclusive 

 of the quartzite, which may elsewhere develop independent importance. . . 

 Its [the limestone's] occurrence on Yakinikak creek is apparently due to 

 down-faulting, as it lies at a comparatively low level among mountains 

 composed of the Algonkian argillites. Its presence in this locality, taken 

 in connection with other occurrences north and south, may be considered 

 evidence of the former extension of the upper Mississippian limestone over 

 the entire region. The absence of earlier Mississippian strata is significant 

 of an unusual overlap.'* 



If this Yakinikak limestone were deposited unconformably upon the Galton 

 (' Algonkian ') series, there must have been strong deformation and extensive 



* B. Willis, Bull. Geol. Soc. America, Vol. 13, 1902, p. 325. 



