156 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



per cent, by weight, of the average rock is quartz. Not a grain of feldspar was 

 seen in thin section and there is a singular lack of the accessories found in the 

 surrounding formations. This quartzite is clearly the most highly silicious 

 member of the Summit series. 



The specific gravities of two type specimens were found to be respectively, - 

 2-655 and 2-661; their average, 2-658, is very close to the average for the whole 

 formation. 



Beehive Formation. 



The Ripple quartzite passes with some abruptness into the conformably 

 overlying Beehive formation, so named after its typical occurrence on Beehive 

 mountain north of Lost creek. Of this formation two complete sections and 

 four other partial sections were traversed. The best exposures within the belt 

 were found on Beehive mountain and on the ridge overlooking, from the north, 

 the south fork of the Salmon river. 



The formation is heterogeneous, yet the recurrence of a rusty-weathering, 

 quartzitic rock-type is so constant throughout the whole mass that it has seemed 

 expedient to include many thousands of feet of these beds tinder one forma- 

 tional name. The total thickness is only roughly estimated but it is believed 

 to be 7,000 feet at a minimum. At Beehive mountain itself there are over 9,000 

 feet of these strata well exposed, but at that section, there is possibly some 

 repetition of beds by overthrusting. As with the majority of the members of 

 the Summit series, suitable horizon-markers for a definite and workable sub- 

 division of the huge sedimentary mass, are very rare. On the western slope 

 of Beehive mountain a 50-foot bed of limestone is included in the field section 

 and will be noted in the columnar section of the formation, but it was not 

 seen outcropping at other localities so as to be a really serviceable horizon- 

 marker. 



A further difficulty in giving a precise lithological description of the forma- 

 tion consists in the relatively high dynamic metamorphism which has affected 

 the mass, especially in the upper part. The only tolerably good exposure of 

 that part, within the belt, occurs on the western slope of Beehive mountain. 

 This section was studied in bad weather and hut a very limited time could 

 be devoted to it, although it is the locality most favourable to the discovery 

 of the principal facts concerning the upper one-third of the formation. At 

 this locality there is apparent conformity with the Lone Star schists, but there 

 is a chance that the appearance is due to the intense mashing which charac- 

 terizes this local area, a dynamic effect whereby the conformity of the schistose 

 structures in the two formations simulates conformity in the dips and strikes 

 of the true bedding-planes. This question of conformity or non-conformity 

 between the Lone Star and Beehive formations cannot be solved with informa- 

 tion now at hand. 



A compilation of the facts derived from the six field-sections led • to the 

 following columnar section. It will be understood that it cannot pretend to a 

 high degree of accuracy. 



