378 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



suit the purposes of the present report. For convenience in discussion and in 

 correlation a few special names are given to the formational groups as defined 

 by Mr. Brock; this is done with the co-operation of Mr. Brock himself. 



The rocks in this part of the Boundary belt are, so far, entirely unfossili- 

 ferous and it is impossible to date the different formations with assurance. 

 The writer's experience during the Boundary survey, especially during the 

 mapping of the Rossland mountains and of tho&e lying between Midway and 

 the Skagit river, has suggested certain correlations with the recognized geolo- 

 gical periods which are somewhat different from those made by Mr. Brock. 

 His chronological table will be reproduced in order to show the differences of 

 conception; the table will at once be useful in illustrating the character of the 

 rocks encountered in the ' Boundary Creek District.' 



Geological Formations of the ' Boundary Greek District ' (Brock) .§ 



Pleistocene).. Glacial and recent deposits. 



(Injections of intrusive sheets, dykes and plutonic masses. Ore deposits, 

 volcanic flows. 

 Tulfs, ash beds, volcanic conglomerates, sandstone and shales, with a 

 little lignite. 



Jurassic ? Granodiorite. 



t> , • , f Serpentine. 



Paleozo.c?.. • j Gr. en porphyrite. 



(Green porphyrite. 

 Volcanic conglomerates, tuffs, ash beds, with arenaceous limestone. 

 Serpentine. 

 Limestones, argillites, quartzite. 

 Crystalline schists? Gneisses and schists. 



Within the five-mile Boundary belt the only rocks corresponding to the 

 Tertiary group listed by Mr. Brock belong to the Midway formation, which is 

 not considered in the present chapter. In the sheet accompanying this 

 report the 'Paleozoic?' volcanic? are mapped under the name 'Phoenix vol- 

 canic group'; the 'Paleozoic?' argillites and quartzites are mapped under the 

 name ' Attwood group ' ; the ' Crystalline schists ?' are recognized as in part 

 made up of a schistose complex, mapped under the name 'Grand Porks group' 

 and for the rest (within the five-mile belt), made up of a highly gneissic 

 granite intrusive into the Grand Porks complex and mapped under the name 

 ' Cascade gneissic batholith.' At Grand Forks these crystalline rocks are cut 

 by a small intrusive stock, mapped under the name ' Smelter granite.' The 

 ' Green porphyrites ' are here mapped with the same colour as the Phoenix 

 group, with which the porphyrites are genetically connected and from which 

 they are very hard to differentiate in the field. 



Grand Porks Schists. 



The dominant country-rocks of the Cascade granite — the Grand Forks 

 schists — include a series of schistose types, which have been completely or 



§ Summary Report, Director of Geological Survey of Canada for 1902, p. 95. 



