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In general the conglomerates are composed chiefly of 

 quartz and quartzose rocks; the sandstones chiefly of 

 granitic detritus, quartz and feldspar; and the shales chiefly 

 of volcanic detritus, being grayish green in color. From the 

 mere statement of these facts, which constitute a rather 

 peculiar feature of the lithology, a simple yet fairly plausible 

 explanation suggests itself. Of all the underlying rocks 

 whose detritus composes the sediments, the volcanic rocks 

 alone were chemically disintegrated, and their detritus, 

 being very fine grained, was deposited as mud which 

 now forms the shales. The granitic rocks were mechani- 

 cally disintegrated, and broken down into a coarse felds- 

 pathic sand, furnishing the material for the sandstones. 

 The quartz veins and the quartzose rocks, however, were 

 broken down only into a coarse rubble to form the material 

 for the conglomerates. 



A peculiar feature of the shale horizons of the upper 

 part of the Nanaimo series, especially of those characterized 

 by a large number of small sandstone interbeds, is the 

 occurrence of numerous sandstone dykes. These cut the 

 shales at all angles to the bedding. They are fairly 

 regular, although branching and offset by faults. The 

 larger, 3 to 4 feet (-9 to 1 -2 m.) thick, may be traced for 

 at least 100 feet (30 m.). Although they cut the shales 

 sharply, apparently along joint planes, the shales are 

 frequently bent or slightly contorted next to the dykes. 

 On the shores, where the dykes are best exposed, on 

 account of their greater resistance to wave erosion, they 

 stand above the shales, forming low walls, the highest 

 wall noted being three feet (9 m.). 



As a rule the dykes are finer grained than the sandstone 

 interbeds, and the cementing material is more calcareous 

 but in general the two are of similar material. Indeed, 

 in many instances, dykes protrude from the sandstone 

 interbeds, and there are off-shoots from the dykes confor- 

 mable with the bedding of the shales, that simulate the 

 appearance of sandstone interbeds, but are recognized as 

 off-shoots by occurring usually on one side of the dyke 

 only. There are also other smaller and more irregular 

 off-shoots into the shales, resembling small apophyses 

 from an igneous dyke. 



From their occurrence and close resemblance to other 

 intrusive sandstone dykes, their origin is in little question. 

 They appear to have been formed by the injection of soft 

 35069— 4B 



