REPORT OF THE CHIEF ASTRONOMER 263 



SESSIONAL PAPER No. 25a 



in diameter or sensibly equal to the average diameter of the grains in the 

 Waterton, Altyn, Siyeh, and Sheppard dolomites. Here as there we have a 

 steady persistence in the size of grain which characterizes the chemically pre- 

 cipitated carbonate. 



The strike and dip of the 450-foot band of dolomite was, on account of the 

 massiveness of the rock, not readily determined but, as usual in the zone, the 

 former was a few degrees east of north, while the dip seemed to be nearly 

 vertical. 



East of the analyzed dolomite, outcrops were few for about 400 feet of 

 cross-section but that stretch seems to be underlain by dolomitic chlorite schist 

 and phyllitic mica schist. Immediately to the eastward and just at the western 

 base of North Star peak, a 200-foot, nearly vertical, band of sheared dirty- 

 white dolomite, weathering yellow, forms the most easterly part of belt B. 

 The strike of the band and of its schistosity planes is about N. 5° E. ; the dip 

 averages 80° E. 



A review of the field-notes suggests that belt B may constitute a closely 

 appressed fold, the erosion of which has produced a duplication of the three dolo- 

 mitic bands on the two sides of the belt. However, the very considerable differ- 

 ences of thickness between the respective bands thus supposed to be duplicated, are 

 so great that one cannot be sure of the postulated repetition. In any case, there 

 is no evidence in this section as to whether the fold is an anticline or a syncline. 

 In no other part of belt B could this point be settled. In the general structure 

 section, therefore, no attempt is made to show the true relations in the great 

 monocline. It has seemed better to illustrate simply the empirical facts of 

 field observation rather than to attempt the projection of folds which, under the 

 circumstances, could be nothing else than fanciful. 



Belt B is, thus, composed of both mica schists and dolomites. In that 

 belt the carbonate rocks are relatively more abundant than in any other belt in 

 the Priest Biver terrane. The persistence of the dolomites along the strike, 

 their nearly vertical dip, the notable straightness of each bed and of the entire 

 belt across North Star mountain, and the general parallelism of belts A and B 

 to the band of Irene conglomerate, would, at first sight, suggest that at least 

 the upper part of the Priest Biver series is conformable to the overlying 

 Summit series. It is believed, however, as noted elsewhere, that this general 

 parallelism of belts A and B to the band of Irene conglomerate is partly an 

 incidental result of the strong upturning and mashing which have forced 

 the two unconformable series into positions of apparent conformity. Six miles 

 north of the Boundary, belt B has been broken by the same fault which offset 

 belt A a mile or more south of Summit creek. At the creek itself the dolomites 

 and schists of belt B are entirely cut off by a second fault (see map) so 

 that these rocks are replaced, north of the Dewdney trail, by the sheared quart- 

 zites characteristic of belt C. 



The dolomitic bands of belt B, like those of belt A, carry small bunches 

 of galena and occasional crystals of copper pyrites. Neither of these ores 

 where they have been actually prospected, as at the claims of ' Copper Camp,' 



