322 DEPARTMENT OF THE INTERIOR 



2 GLuKGE V, A. 1912 



greenstones occurring in the Pend D'Oreille group (especially those near the 

 Columbia river) are of the same age. The quartzites and slaty rocks of the Pend 

 D'Oreille group are almost if not quite indistinguishable both in composition 

 and in degree of metamorphism from the quartzites and slates interbedded with 

 the greenstones of the Rossland mountains. The Pend D'Oreille marbles are 

 lithologically identical with the obscurely fossiliferous limestones just described. 

 As the best working hypothesis, therefore, the writer is inclined to believe that 

 the western slope of the Selkirk range and the eastern half of the Columbia 

 system are underlain by residuals of a very thick upper Paleozoic, probably 

 Carboniferous, series which represents the oldest sedimentary rocks of those parts 

 of the Boundary belt. It will be seen that the same series probably has similar 

 fundamental relations in the Midway and more westerly mountain groups. 



Mesozoic Sediments at Little Sheep Creek. 



At Monument 175 in Little Sheep creek valley, erosion has laid bare a con- 

 siderable thickness of stratified rocks which are evidently much younger than 

 the marbles and quartzites farther up the valley. The exposures are not good 

 but, since these younger rocks are also obscurely fossiliferous, the field observa- 

 tions so far made may be detailed. At the Boundary monument the steep slope 

 of Malde mountain is seen to be largely underlain by black and red argillite, 

 enclosing thin beds of gray sandstone and of angular conglomerate, as well as a 

 number of layers of sandstone which is described in the field notes as hard 

 black quartzite. The quartzite is sulphide-bearing. These beds are greatly 

 deformed, the argillite specially showing frequent changes of strike and dip in 

 short distances both up the slope and along its foot. The more rigid sandstone 

 beds tend to have a fairly steady strike of N. 0°-10° E., with an average dip of 

 from 35° E. to 90°. The series, chiefly argillitic, continues eastward to a contour 

 about 600 feet above Little Sheep creek, and there it appears to dip under the 

 volcanic breccias of Malde mountain. This general eastward dip appears to 

 characterize the series throughout its extent of 600 yards ixp the valley from the 

 Boundary slash. The exposures south of the line did not promise useful results 

 and the beds were not followed in that direction. The exposures are likewise 

 very poor on the west side of the creek, but the shale-sandstone series seems to 

 extend on the Sophie mountain slope at least 500 feet above the creek. The 

 argillite is there greatly crumpled, but probably strikes in the average direction, 

 N. 65° E., with dip high to the northwest. 



The series seems thus to be at least 600 feet thick and to have the attitude 

 of a broken and mashed anticline plunging to the north, carrying the sediments 

 beneath the Malde mountain and Sophie mountain breccias and lavas. The field 

 relations are, however, so obscure that this conception must be regarded as only 

 suggestive and by no means proved to be correct. 



At the rock-bluffs along the railway track and on each side of the Boundary 

 slash, a number of very poorly preserved remains of plants were found in the 

 shales. These fossils were submitted to Professor D. P. Penhallow, who iden- 

 tified them l as the rachises of a fern, in all probability of Gleichenia (gilbert- 



