REPORT OF THE CHIEF ASTRONOMER 485 



SESSIONAL PAPER No. 25a 



great, is believed to be a minimum. This member is best seen on the trail up 

 Castle creek; there abundant, though not well preserved fossils, both shells and 

 plants, were found at a horizon about 200 feet below the top of the member. 

 These fossils will be described on succeeding pages. 



The overlying black argillite member I, is, so far as known, unfossiliferous. 

 It very clearly overlies member H and underlies the conglomerate of member J. 



On account of its coarseness and great thickness — 1,400 feet — member J 

 is a very conspicuous element of the series. It was traced continuously from 

 the summit north of Castle creek to a point well south of the Boundary line. 

 Throughout that distance the conglomerate preserves a strike averaging about 

 1ST. 22° W., and a dip of from 60° to 65° to the west-southwest. This steady 

 behaviour of so prominent a member tended to make the structural study of the 

 formation west of the Chuchuwanten comparatively easy. Its occurrence only 

 once in the wide monocline has been a principal reason for believing that pro- 

 nounced duplication of strata by strike-faults has not taken place. 



This conglomerate is usually coarse; the pebbles reach eighteen inches or 

 more in diameter. They are highly diverse in character. The list of different 

 materials is long, including: gray, banded quartzite; blackish quartzite; hard, 

 black and gray argillite; gneissic and massive hornblende granite; white aplitic 

 granite; biotite granite; syenite porphyry; amphibolite; fine-grained diorite; 

 coarse hornblende gabbro; greenstone schist; sericite schist; aphanitic quartz 

 porphyry; and a breccia composed of white quartz fragments with jaspery 

 cement. This list shows that most of the staple pre-C'retaceous formations of 

 the region are represented. Among the granitic pebbles were a considerable 

 number having the composition of typical, fresh Eemmel granodiorite or quartz 

 diorite in its Western phase. Both the hornblende and the large, lustrous-black 

 crystals of biotite in the Eemmel are to be seen in these pebbles. The latter 

 must have been derived from fresh, little weathered ledges. 



The cement of the conglomerate is a green feldspathic sand essentially like 

 the green sandstones overlying and underlying this great conglomerate member. 

 The cement yields rather readily to the weather, so that long talus-slopes of the 

 weathered-out pebbles fringe the many cliffs where the conglomerate crops out. 



Towards the top the conglomerate grows finer-grained and merges into the 

 very thick sandstone member K. This sandstone forms a continuous band cross- 

 ing the Boundary belt. The band is a little over two miles wide and the average 

 dip is about 45° to the west-southwest. The calculated thickness — 7,100 feet — 

 is again enormous but it is a minimum. Three cross-sections of the wide band 

 were traversed. In none of them was there any sign of repetition of beds nor 

 any serious departure from the average strike and dip. The uniformity in the 

 width of the band is another indication of the absence of strong faulting within 

 the area covered by this member. 



The sandstone of K is a hard, green to gray, brown-weathering, feldspathic 

 lock much like those in members D, F and E. It i? interrupted by numeroiis 

 beds of black to rusty argillite and argillaceous sandstone and is itself often 

 more argillaceous than the average sandstone of the older members. Thin lenses 



