REPORT OF TEE CHIEF ASTRONOMER 545 



SESSIONAL PAPER No. 25a 



northern limb of the McGxiire mountain syncline. The east-west direction of 

 these axes may possibly be connected genetically with the east-west course of the 

 wide Eraser valley to the north. 



Elsewhere the only observed structures in the stratified rocks are local 

 crumples, faults, and small thrusts. Of these, normal faults seem to be most 

 important in explaining the actual distribution of the rocks now exposed. As 

 noted long ago by Bauerman, the section up the Chilliwack river seems to be 

 that of a gigantic monocline, showing an almost incredible thickness of Paleo- 

 zoic rocks. This is probably a deceitful appearance. East of the nose of the 

 supposed anticlinal near Slesse creek a heavy, crinoidal limestone with moderate 

 northeasterly dip appears four times in the river section, besides appearing in 

 the northern limb of the anticline. The writer is inclined to regard this lime- 

 stone as representing the same horizon throughout ; if so, it is best to suppose 

 that the repetition of the limestone, with the associated shales and sandstones, 

 is due to normal faulting. The faults are probably strike-faults, running in a 

 general northwesterly direction; the downthrow being on the southwest in each 

 of the four displacements postulated. It should be added that the exposures are 

 so poor that this partial explanation of the great thickness of beds outcropping 

 along the Chilliwack river is in high degree still hypothetical. 



Somewhat more certain is the necessity of mapping the faults bounding 

 the Triassic Cultus formation on east and west. The one on the west seems 

 proved rather clearly; the other is not proved as to its actual location, but has 

 been entered on the map to explain in this case the relation of fossiliferous 

 Mesozoic and Paleozoic strata in lateral contact. 



The faults limiting the Skagit volcanics on north and west as well as at the 

 Skagit river, have already been mentioned; little doubt is felt as to the exis- 

 tence of all three of these master displacements. 



Nothing need be added to the descriptions of the structural relations of the 

 granitic bodies, as already given in the respective* sections of the present chapter. 

 The cardinal fact of magmatic replacement of the huge Paleozoic geosynclinal 

 prism as well as the pre-Cambrian basement terrane by the Chilliwack batholith, 

 and also by the Custer batholith if it is of Jurassic date, seems to the writer 

 quite obvious in the field. The relations are precisely the same as those stated 

 for the vast Coast range batholith, described by Dawson, Lawson, and the geolo- 

 gists working in Alaska, except that the Chilliwack batholith is probably younger 

 than its great neighbour. Nearly all of these observers agree as to the fact of 

 the replacement for the Coast range batholith. The significance of their agree- 

 ment is great, for they have studied the world's greatest post-Cambrian batho- 

 lith invading one of the world's greatest geosynclinals. 



CORRELATION. 



The geological dating of the various formations observed in the Boundary 

 belt where it crosses the Skagit range, has already been discussed in connection 

 with the description of the more important rock-bodies. Many doubts remain 

 as to the exact order in which they should be arranged in the geological time- 



25a— vol. ii— 35 



