274 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



A strong* cataclastic structure was microscopically observed to be a general 

 feature of the marble. 



It is impossible effectively to distinguish the true stratigraphic positions 

 of all the marble bands in the area, or to be sure of their correlation among 

 themselves. They are, therefore, mapped under the common name, " Pend 

 D'Oreille limestone.' 



Between the mapped monzonite stock and the Salmon river flat the quartz- 

 ite-phyllite bears one or more strong intercalations of amphibolite, composed of 

 dark olive-green hornblende, quartz, and highly granulated residual individuals 

 of basic plagioclase. Other intercalations of amphibolite and hornblende schist 

 were observed on Lost creek just above its confluence with Lime creek, and on 

 the Salmon river below Roseleaf creek. 



Throughout the four-mile section the dips of the schistosity planes are 

 generally high (40° to 75°) to the eastward, though they are, of course, often 

 reversed in the numerous crumples affecting the schists. The banding of the 

 limestones and their planes of contact with the schist were usually seen to dip 

 eastward at similarly high angles. The attitude of the bedding-planes cannot 

 be taken as directly indicating the succession from older to younger in this 

 sedimentary monocline; there is every possibility that the whole group has 

 been overturned along with the apparently conformable Lone Star and Beehive 

 members of the Summit series. In favour of this conception is the fact that 

 a massive limestone of great thickness, of similar lithological characters, and 

 lying nearly flat, overlies a thick series of phyllitic and quartzitic rocks between 

 Roseleaf creek and the Pend D'Oreille river. This limestone covers at least 

 five square miles and dips from 10° to 30° south; it is highly improbable that 

 so larg;e a mass has been overturned. The underlying schists are in the main 

 like those exposed in Lone Star mountain. The tentative conclusion has 

 thus been reached that the schistose rocks composing the Lone Star section 

 from the western contact of the Lone Star schist to the eastern contact of the 

 great limestone band all underlie that limestone and, with it, have been over- 

 thrown so as now apparently to overlie the limestone. On the same tentative 

 basis these older schistose sediments may be set down as totalling at least 

 3,500 feet in thickness. 



The large body of marble situated at the confluence of Lost creek and the 

 south fork of the Salmon river is probably the down faulted equivalent of the 

 2.000-foot band of limestone above described. If so, the phyllites and quartzites 

 lying to the westward of that band may be wholly or in part of the same age 

 as the schists lying to the eastward of the band. In this Lone Star-Salmon 

 river section, therefore, one cannot be sure that there are any sediments 

 younger than the great limestone. Unfortunately, no other area in the Boun- 

 dary belt has afforded any more certain help in carrying the stratigraphic 

 succession higher or completing the columnar section for this region. It is 

 probable that the micaceous schists exposed in Sheep Creek valley for three 

 miles from its intersection with Salmon river, are younger than the great 

 limestone, but the exposures are much too imperfect to warrant a definite 

 conclusion on the point. 



