516 DEPARTMENT OF PHE INTERIOR 



2 GEORGE V., A. 1912 



Girty. The estimated thickness given above for the sediments of the series — 

 6,780 feet — is the minimum thickness of the Upper Carboniferous sediments in 

 this region. 



Cultus Formation. 



Sttfatigfaphy mid Structure. — In 1859 Bauerman recognized the strong 

 lithological contrasts between the rocks on the two sides of Cultus lake and 

 remarked that the distinctly more metamorphosed sedimentaries on the west 

 side looked geologically older than the shales and sandstones of the eastern 

 shore. The writer is inclined to share Bauerman's view and, as noted above, 

 tentatively maps the rocks of Cultus ridge, as well as the large area of (fossili- 

 ferous) argillite to the southeast of that ridge as Triassic, while the beds 

 occurring in Vedder mountain are mapped as Carboniferous. The name, Cultus 

 formation, may be advantageously given to the younger group of strata. It 

 may be defined as the local series of sediments which belong to the same geologi- 

 cal system as the thick argillite bearing the Mesozoic fossils of lot No. 1502, 

 hereafter described. 



The dominant rock of the formation is a dark gray to blackish argillite, 

 often bituminous in moderate degree. With it there are generally associated 

 thin or thick bands of gray or greenish-gray sandstone and grit, and, more 

 rarely, interbeds of fine conglomerate. The gritty beds are characteristically 

 charged, very often, with small angular fragments of black argillite. All the 

 coarser-grained types tend to be decidedly feldspathic, sometimes suggesting an 

 arkose. These rocks are invariably deformed, with dips running up to 70° or 

 80°, though those of 30° or 35° are the commonest. The strike is highly 

 variable in many places but the average direction is that parallel to the Cultus 

 Lake valley; the average dip of, say 30°, is to the southeast all across the area 

 where the formation is mapped. The argillites are very often heavily slickened 

 by local faults but the formation as a whole cannot be described as much meta- 

 morphosed. Phyllitic phases, for example, were not discovered. This relative 

 lack of metamorphism was one of the criteria by which the formation was 

 separated from the argillaceous phases of the Chilliwack series. As Dawson 

 found in Vancouver island, the difficulty of distinguishing the Paleozoic and 

 Mesozoic beds is greatly enhanced by the fact that in both, argillaceous types 

 of great similarity ini their original composition are the dominant types. 

 Needless to say, the future worker in the geology of the lower Chilliwack valley 

 will not take the accompanying map too seriously but will regard it as simply 

 the first rough approximation in mapping. Incidentally, the present writer 

 anticipates with great sympathy the struggle of such future worker with the 

 jungle beneath which the truth is here hidden. 



Two great normal faults and a no less important over-thrust are entered 

 on the map as explaining the lateral relations of the block of Cultus sediments 

 with the surrounding Chilliwack formations. These suggestions will need 

 special scrutiny. 



