486 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



of fine-grained conglomerate also occur' at intervals. One of these, about 2,000 

 feet below the top of the member, carries fossil shells. A few feet away from 

 the locality where the large shells were found, the sandstone encloses plant- 

 remains. From the eastern end of the Castle Peak stock of granodiorite to the 

 Lightning creek fault — a distance of nearly ten miles — the greater part of the 

 Boundary belt is underlain by the black argillite of member L. The strata 

 here show dips varying from 25° to 90°. As already noted it has not proved 

 feasible to work out the folds and faults with entire confidence; in consequence, 

 the thickness of the argillite is in doubt. It is known, however, that it must be 

 at least 3,000 feet and may, as estimated in the field, be more than 5,000 feet. 

 At its base it grades rapidly into the conformable sandstone member K. 



Member L is a rather homogeneous, hard, black or dark-gray shale, in which 

 thin, green and gray sandstone beds are intercalated. The shale weathers gray 

 and brown in varying tints. At three horizons, — one found opposite the mouth 

 of Pass creek, another 700 yards south of the 7,860-foot summit overlooking the 

 creek, and the third on the ridge 1,000 yards east of Prosty Peak, — the shale 

 carries fossil plants and ammonite impressions. 



Granitic intrusions have to some extent metamorphosed the argillite. The 

 metamorphic effect is apparently most pronounced about the Castle Peak stock, 

 though the effects are nowhere very striking. The shale inclusions in the stock 

 have been converted into hornfels of common type. 



Fossils Collected. — It has been seen that the monotonous chain of failures 

 in the many efforts to discover fossil remains along the Porty-ninth Parallel 

 was seldom broken. The decided novelty of finding them at several horizons 

 within the Pasayten series was specially welcomed, as these discoveries bade fair 

 to clear up many points in the dynamic history of the eastern half of the 

 Cascade mountain system and incidentally to throw light on the history and 

 relations of unfossiliferous formations in the broad Columbia system as well. 

 Many of the correlations noted in preceding chapters have, in fact, been made 

 in the light of the analogies which may be traced between the structure and 

 stratigraphy of the more easterly ranges and the more closely determined struc- 

 ture and stratigraphy of the Hozomeen range. 



The conditions of field work during the Boundary survey did not permit of 

 exhaustive collections at any point. As a guide to the future paleontological 

 study of the Pasayten series the exact localities of the different collections of 

 plant and animal remains will be noted. Each locality will be referred to by 

 the corresponding specimen number. In connection with each the stratigraphic 

 and paleontological details will be added. 



No. 11$8. At the 6,750-foot contour 400 yards southeast of the 6,920-foot 

 peak situated two miles north of the Boundary line and about three miles west 

 of the Pasayten river. 



Stratigraphic position: about 3,500 feet above the base of member B. Sand- 

 stone with shaly interbeds. 



