0. II. Hershey — Belt and Pelona Series. 265 



white quartzite, generally of coarser grain than qnartzites in 

 higher formations. I have no means of determining the thick- 

 ness of the Prichard in this district, but I am not disposed to 

 criticise Calkins' estimate of 8,000 feet for the Coeur d'Alene 

 District as a whole. 



At the top of the Prichard formation there is a rock made 

 up of dark bluish-gray argillite and whitish arenaceous mate- 

 rial in very thin alternating laminae. This passes by transition 

 strata into the Lower Burke division, the best section of which 

 is on the southern side of Kellogg Peak. The predominating 

 type is a greenish, thin-bedded sericitic quartzite, the darker 

 jjreen bands of which appear quite strongly chloritic. Layers 

 of hard, white, heavy-bedded, poorly sericitic quartzite, 2 to 6 

 feet thick, alternate with greenish sericitic quartzite and are 

 quite numerous, though they constitute a comparatively small 

 part of the Lower Burke member. In this section there is not 

 much purplish material, but elsewhere in the district, particu- 

 larly in the Deadwood Gulch region, there is much purplish 

 gray, thin-bedded quartzite and shale which locally may attain 

 a thickness of several hundred feet, though generally inter- 

 bedded with greenish layers. My impression is that they 

 characterize the upper portion of the Lower Burke. Litho- 

 logicaily they are indistinguishable from the purplish gray 

 quartzites and shales of the St. Regis formation except that, 

 1 think, they are harder and less shaly than the latter. These 

 purplish gray horizons have given me more trouble in the 

 mapping of the Wardner District than has any other type of 

 rock. The thickness of the Lower Burke member is about 

 1500 feet. 



The Upper Burke member consists of an alternation of 

 thin-bedded, greenish, sericitic quartzites and heavy-bedded, 

 white, nearly pure quartzites. The first type of rock is gener- 

 ally softer, thinner bedded, and of a lighter green than the 

 typical greenish gray Lower Burke quartzite. The heavy- 

 bedded white quartzites microscopically resemble the white 

 quartzites of the Revett formation, but they break down rap- 

 idly under weathering agencies and give rise to much fine 

 yellowish quartzite debris. Underground, they are in places 

 hard and flinty and in others have lost the cementing material 

 and become an incoherent pure white sand. I draw the base 

 of the Upper Burke at the bottom of the first heavy bed of 

 such quartzite ; this is usually 30 to 50 feet thick, though in 

 one section it is 300- feet thick. The thickness of the Upper 

 Burke member is about 2,000 feet, making 3,500 feet for the 

 Burke formation as against 2,000 feet for the formation in the 

 eastern part of the Coeur d'Alene District as estimated by 

 Calkins. My impression is that the thinning eastward is at 



