SEDIMENTS IN THE DELTA OF ERASER RIVER 121 



the lake have a maximum range of about 3I feet, and there are 

 strong currents both ways. The delta is being built into the lake 

 at the south end, although the drainage of the lake basin is outward 

 or toward the south. This is the case because the inward, flood- 

 tidal current is stronger than the outward current, because the 

 rise of tide on the flood is more rapid than the fall on the ebb, and 

 the outflow of river water is not great enough to counteract this 

 effect. 



The delta is partly submerged and extends about 4 miles into 

 the south end of the lake. The top-set beds are exposed in places 

 at extreme low tide, but are for the most part covered by 3 to 6 feet 

 of water. A single, straight river channel extends through the 

 delta. The delta has advanced along the line of the channel and 

 left unfilled a deep depression on its west side. The fore-set beds 

 are well developed and extend to depths of 20 to 30 fathoms, the 

 slope being in places as much as 30°, but for the most part only 

 about 10°. The lake has a maximum depth near its south end of 

 about 50 fathoms. In the narrow parts near the north end the 

 maximum depth is about 80 fathoms. 



CHARACTER OF STRATIFICATION OF THE SEDIMENTS 



A number of core samples of bottom deposits in the Strait of 

 Georgia, off the mouth of the Fraser and in Pitt Lake, were obtained 

 by means of a bottom-sampling machine. The machine consisted 

 of a hollow casting, 3 feet long, sharpened at the lower end and 

 fitted at the top with a ball valve which worked automatically. 

 The machine weighed 55 pounds and was operated from a motor 

 boat by means of a sounding machine of the ordinary type. The 

 samples were mounted in plaster of paris and sectioned vertically 

 to show the character of the stratification. A number of the 

 samples are shown in Figures i and 2. 



The stratification of the top-set beds of the Fraser Delta and 

 alluvial flood-plain deposits differs in different parts of the vertical 

 section. Below the level of mean low tide the top-set beds are 

 composed largely of sand, are for the most part horizontally bedded, 

 but in places are cross-bedded and current-ripple-marked. In 

 places there are thick and thin lenses or beds of silt and clay which 



