I20 W. A. JOHNSTON 



30-fathom line the beds slope more gradually seaward, the 100- 

 fathom line being reached at from i to 2 miles from the outer edge 

 of the sand banks. The horizontal bottom-set beds, consisting of 

 very fine material, occupy the bottom over a considerable part of 

 the Strait of Georgia, off the mouth of the river. The strait, 

 which is 10 to 15 miles wide, varies in depth in its central part 

 from 100 fathoms to about 225 fathoms. The top-set beds are 

 thinnest and in most places only a few feet in thickness. In 

 places, however, they may be upward of 100 feet thick, as, for 

 example, where a deep channel of the river has been abandoned 

 and has been gradually filled and built up to high-tide level. The 

 top-set beds are sandy in character in their lower part up to about 

 half-tide level, the upper part being silty in character. The silty, 

 fine-grained beds, formed by deposition from flood waters over- 

 flowing the river banks, become thicker, progressively, upstream, 

 owing to the fact that freshet waters do not affect the level of high 

 tide in the lower part of the river as far up as Steveston, 6 miles 

 above the mouth, but appreciably affect the level in the upper part 

 of the river. The shore face of the delta is very weakly developed 

 because wave action has little effect owing to the shallowness of 

 the water over the sand banks. 



The river, for a distance of 40 miles above New Westminster, 

 is in places bordered by extensive flats, mostly below high-tide, 

 freshet level, which have been formed by the meandering of the 

 river and its tributaries, and by deposition from flood waters. The 

 flats, for the most part, have been carved out of the raised 

 Pleistocene marine clays and delta deposits and form the alluvial 

 flood plain of the river. 



PITT LAKE DELTA 



An unusual kind of delta is being formed at the lower or south 

 end of Pitt Lake, which drains south by way of Pitt River into the 

 Fraser above New Westminster. The lake is ^ to 2^ miles wide 

 and 15 miles long, and is tidal. During the freshet stage of the 

 Fraser the surface of the water in Pitt River and Pitt Lake is 

 raised several feet above the normal level and falls only slightly 

 with the tides, so that during this time there is very little current 

 into or out of the lake. During the low-water stage, the tides in 



