REPORT OF THE CHIEF ASTRONOMER 269 



SESSIONAL PAPER No. 25a 



nor a single one of about one hundred specimens, more closely studied in the 

 laboratory, is without abundant signs of crushing or, at least, recrystallization. 



The carbonate rocks occur in belts A, B, and C, but are chiefly concentrated 

 in belt B. In the section crossing that belt, northwest of North Star mountain, 

 the six great beds of the dolomitic marbles aggregate about 1,500 feet in thick- 

 ness. If the three beds outcropping on the western side of the belt are but 

 duplications of the three beds outcropping on the eastern side, and, if half the 

 mean of the thickness be assumed as indicating the real thickness of the three 

 beds, this would total 750 feet. In belts A and C there must be at least 250 

 feet of highly magnesian rock additional. The writer believes, in fact, that 

 1,000 feet represents the minimum thickness of the total dolomitic rock as 

 exposed rn this area of the Priest River terrane. 



Most of belts A and G and a large part of B are composed of rather homo- 

 geneous mica schists, including great' masses of phyllite and chloritic schist. 

 It is possible that belt B represents a duplication of A; with this assumption 

 a very rough estimate of the minimum total thickness of the argillaceous strata 

 corresponding to these schists is 5,000 feet. 



The thicknesses of the dominant quartzites of belts D and F, which are. 

 lithologically very similar, are extremely difficult to estimate but it is believed 

 that at least 6,000 feet of different beds must be represented. The total appar- 

 ent thickness of the spangled schist is over 6,000 feet and an estimate of 3,000 

 feet, based on the possibility that belt E coincides with a simple closed vertical 

 fold, seems to be a safe minimum estimate for the thickness of the spangled 

 schist. Belt G consists of mica schists which in several respects are very 

 similar to the schists of belts A, B and G, yet no dolomites have been found 

 in belt G and it would be unsafe to correlate the strata of belt G with those of 

 any of the western zones. In any case, it appears that at least 3,000 feet of 

 reciystallized strata, not appearing in any of the members estimated above, 

 must be added to complete the total of strata exposed in the area. 



It thus seems likely that this total is, at the minimum, 18,000 feet. Even 

 that estimate is large in absolute measure but the total number of feet is but 

 a relatively small fraction of the apparent thickness of the whole series. Rough 

 as the estimate is, it indicates the fact, amply demonstrated by the field obser- 

 vations, that this old series is of great thickness even when compared with the 

 more certain minimum totals for the neighbouring Summit and Purcell series. 



At one stage in the work of interpreting the terrane it was postulated that 

 at least part of belts D, E, F, and G really form part of ihe Cambrian-Beltian 

 series, being thus equivalent to the quartzitic and argillaceous phases of the 

 Summit and^ Purcell groups. A careful study of the field data and of the col- 

 lection of specimens has, however, led the writer to believe that this supposition 

 is inadmissible. Quite apart from the thermal action of the Rykert and Bayonne 

 batholiths, the whole Priest River terrane is intensely metamorphosed, to a 

 degree never seen in the Purcell series and only rarely, and then but locally, 

 observed in the Summit series. Moreover, the detailed composition of none 

 of the belts agrees with any similarly thick portion of the Summit or Purcell 



