126 W. A. JOHNSTON 



and the beds are probably thick and massive. As the samples 

 from the bottom-set beds were taken at points where sedimenta- 

 tion is taking place at the rate of at least i foot per year, they 

 cannot be taken as criteria of the presence or absence of seasonal 

 banding. It is possible that in places the bedding is seasonal in 

 character, for coarser material is carried out into the strait during 

 the freshet than during the low-water stage of the river. 



Samples from the bottom of Pitt Lake are shown in Figure 2. 

 Sample No. 12 is from the submerged top-set beds, samples Nos. 

 13 and 14 are from the inclined fore-set beds, and samples Nos. 

 15 and 16 are from the bottom-set beds of the delta at the south 

 end of the lake. Sample No. 17 is from the bottom-set beds of 

 the delta formed by inflowing streams at the north end of the lake. 



The character of the stratification of the deposits formed in 

 the tidal fresh-water body differs in several ways from that of the 

 deposits formed in salt water in the Strait of Georgia. Tidal 

 laminae are shown to some extent in all the samples from Pitt 

 Lake. They are exceedingly fine, being in places as many as 100 

 to the inch. The bedding of the fore-set beds is much more even 

 than that of the fore-set beds of the Fraser Delta, apparently 

 because of the absence of tidal currents along the front of the 

 delta. Samples Nos. 13, 14, and 15 (Fig. 2) were taken at the 

 south end of the lake near the subaqueous front of the delta. 

 They all show a fairly regular recurrence of silty layers (light- 

 colored) separated by sandy layers (dark colored) . This banding 

 is probably tidal in character and may be explained as follows. 

 There are two tides daily in Pitt Lake, but one is so small that as 

 a rule the current is not reversed; so that there is nearly always 

 only one period of outflow and one of inflow each day. Large 

 tides occur twice a month near the times of maximum declination 

 of the moon, and small tides occur near the times when the moon 

 is over the equator. The inward current is greater at the period 

 of large tides than at that of small tides. During the times of 

 large tides sand tends to be deposited, and during the times of 

 small tides silt tends to be deposited. The sandy bands separating 

 the silty bands are very thinly laminated and in places contain 

 eight or ten laminae. The silty bands also are in places thinly 



