398 REPORT UNITED STATES GEOLOGICAL SURVEY. 



sedmientaries indicating snch to be the case. Therefore, "with the de- 

 scription of this escarpment exposure, the section is carried to the sum- 

 mit of Mount Caribou, and is as follows : 



132. Drab shales, metamorphosed into brittle slates, exposed 50 feet, 

 the base concealed beneath the upper rim of the talus accumulation. 



133. A heavy ledge of decomposing greenish gray intrusive rock re- 

 sembling basalt, enclosing hard pebble-like bodies of hornblendic trachyte ; 

 about 25 feet. 



134. Drab, green, and chocolate-tinted shales ,changecl by metamorphic 

 action to a brittle slate, a heavy deposit, in the aggregate about 365 feet, 

 which was deposited consecutively with that portion mentioned under No. 

 132, from which it was subsequently separated by the intrusion of the vol- 

 canic matter No. 133. This deposit presents the following subdivisions : 

 a. The lower 75 to 100 feet shows at the bottom and top buff sandstone 

 layers, and distributed through the mass of the slate occur apparently 

 irregular bands or "pockets" of rusty, porous " mineral "-like material, 

 which doubtless owes its origin to volcanic action, b. Drab, greenish- 

 tinged metamorphosed shale, about 100 feet ; dip 25° to 35°, S. 60° W. 

 c. Laminated sandstone, 5 feet exposed, probably thicker, interlaminated 

 with shales, d. Irregular lenticular or "pocket "-like masses of brown 

 or rusty gray "mineral" rock included in metamorphosed shale, associ- 

 ated with calcite, distributed through a thickness of about 60 feet. e. 

 Thin intrusive sheet of porphyrinic (?) rock, 3 feet. /. Chocolate-drab, 

 metamorphosed shale, about 60 feet. 



135. A heavy deposit, apparently consisting of a brecciated conglomer- 

 itic mass caught up in the intrusive material, with green copper-stained 

 pyritous ' l pockets," and presenting an inferior rusty porous portion, darker 

 purple middle layer, and greenish-tinged upper portion, in the aggregate 

 about 100 feet thick j dip 45° southwestward. 



136. Drab and gray, rather uniformly fine textured limestone, appar- 

 ently partially metamorphosed and fragmentary, exposed 30 to 75 feet. 

 In the saddle to the southeast of the summit, and at a lower level, the 

 ledge dips at an angle of about 30° S., 45° W. It contains a small 

 Gasteropod, but too imperfect for further determination than to note its 

 resemblance and probable specific identity with the but little better 

 preserved specimens of the shell occurring in bed 112. This rock out- 

 crops in the saddle west of, and intervening between, the summit at the 

 station and the slate-capped prominence of the great west spur. It is 

 here much changed by metamorphism, probably by contact with, or 

 proximity to, the eruptive mass of which the bulk of this spur is com- 

 posed. 



137. Greenish gray decomposing ferruginous intrusive mass, resem- 

 bling rotten basalt, and belonging to a debatable series of volcanic prod- 

 ucts. About 6 feet. 



138. Highly metamorphosed drab, brittle shale, thickness undeter- 

 mined, crowning the summit and occurring in patches in the shelving 

 western portion of the main mountain. 



From the latter point our examinations of the slopes on the western 

 flank, or John Gray's Lake drainage, were carried along a line a couple 

 of miles southeast of Station XXVIII, commencing at the summit of 

 the lower mountain ridge, which constitutes the southeastern prolonga- 

 tion of Mount Caribou. The initial horizons at the latter point were 

 not positively identified with any member of the foregoing section ; but, 

 taking into account the bearing of the ledges in Station XXVILT, it 

 seems very probable that the two localities are stratigraphically identi- 



