452 W. A. Johnston — Delta of Fraser River. 



mately at one point by a well boring at Steve st on on 

 Fraser river, 5>4 miles upstream from the seaward front 

 of the delta. The man who drilled the well stated that 

 sand was passed through for a depth of 700 feet from the 

 surface, a bowlder 10 feet in diameter was penetrated at 

 710 feet, and the first stratum of hard shale was encoun- 

 tered at 860 feet. The Recent delta is probably, there- 

 fore at least 700 feet thick at this point. 



An estimate of the yearly rate of seaward advance of 

 the delta for the past 60 years has been made by Mr. W. 

 H. Boyd, Chief Topographer of the Geological Survey 

 Branch, Department of Mines, Canada, by a comparison 

 of the soundings made in 1859 and shown on the 1860 

 chart with those made in 1919 by the Hydrographic Sur- 

 vey of Canada. The advance seaward of the bottom of 

 the steep under-water face of the delta, which is marked 

 approximately by the 30-fathom line, was determined by 

 a comparison of soundings made in 1859 with those made 

 in 1919. The rate of advance thus determined was taken 

 as the rate of advance of the delta. The results showed 

 that there has been no advance in the southern (one-third) 

 part of the delta front, the reason for this being that the 

 flood-tidal current sweeps this part of the delta and com- 

 paratively little sediment has been delivered by the river 

 to this part. In the central part, for a distance of 4^^ 

 miles, the rate of advance is considerable, the average of 

 all the rates of advance, as determined at different points, 

 being 26 feet a year. At one point the rate of advance 

 was found to be 50.6 feet a year. The rate of advance 

 at this point, however, is probably representative of only 

 a very small part of the delta front. Discarding it, the 

 average rate of advance a year of the central part of the 

 delta is 20 feet per year. The northern (one-third) part 

 of the delta front has also advanced because the entrance 

 of the North Arm of the Fraser is in this part of ^ the 

 delta and the flood-tidal currents tend to carry northward 

 part of the sediment brought down by the main Fraser. 

 The average rate of advance of the northern part of the 

 delta is probably about half that of the central part but 

 is not definitely kno^\m because of the lack of sufficient 

 soundings for purposes of comparison. The average 

 rate of advance of the delta as a whole is probably, there- 

 fore, about 10 feet a year. 



The age of the Eecent delta may be approximately 



