321 



on a surface of considerable relief, and under varying 

 conditions, as shown by the rapid lateral and vertical 

 gradation of the sediments. The series also contains 

 land plants and coal, probably of fresh water accumu- 

 lation. Hence conditions of fresh or at least brackish 

 water, that is, terrestrial conditions, alternated with 

 marine conditions. The upper part of the Nanaimo series, 

 however, contains few or no marine organisms, the only 

 fossils being a few obscure plants. It is possible therefore, 

 that the alternating conditions recorded in the lower part 

 of the Nanaimo formation were finally replaced entirely 

 by terrestrial conditions. The lithological character of 

 the sediments — the sandstone being composed of angular 

 to sub-angular fragments and of a large percentage of 

 easily decomposed minerals such as feldspar — indicates 

 a very rapid accumulation and deposition in relatively small 

 basins, where the detritus was not subject to severe wave 

 action. The sedimentation began in Upper Cretaceous 

 time, at a stage corresponding with the Chico, or the Pierre, 

 and it appears as if the sediments were first deposited in 

 a marine basin, between the mainland and Vancouver island, 

 which basin was probably one of deformation, depressed 

 at least as early as the upper Jurassic. During the 

 deposition, the sedimentation trangress^d inland, at 

 first filling up the irrgularities of the pre-Upper Cretaceous 

 erosion, and then possibly covering even the higher residual 

 elevations. The total thickness of the Nanaimo series 

 was near 10,000 feet (3,000 m.) toward the close of its 

 deposition, at which time it extended far inland over the 

 denuded crystalline rocks covering the greater part of 

 the island, or was perhaps restricted to large depressions. 

 The conditions of deposition in the northwestern part of 

 the Nanaimo basin, where the coal deposits occur, appear 

 to have been more uniform than these which existed else- 

 where, for there the series may be subdivided solely on a 

 lithological basis into various formations each with its 

 more or less peculiar characteristics. The formations are 

 enumerated and their thickness and general lithological 

 character given in the following table: — 



