E. M. Kindle—Pit and Mound Structure. 543 
experimental work has been done on this subject by Reade and 
Holland.! They have tried a large variety of fine clays. From these 
standard turbidity preparations of water were prepared in which 
weight of fine clay ina given volume was known. To these were added 
as precipitants in their experiments: (1) sea-water, (2) calcium 
dicarbonate, and (8) calcium sulphate. Equal volumes of precipitant 
and muddy water were mixed, and time of flocculation and complete 
clearing noted. Flocculation was always far more rapid than in the 
case of untreated water. The work of these and other authors has 
clearly shown the effect of salt and other constituents of marine waters 
in accelerating sedimentation. 
In the following experiments, which were made at air temperatures 
with the fine-grained blue Pleistocene clay of the Ottawa Valley, 
attention will be directed to the action of the vertical currents which 
are developed during the deposition of clay sediment in the presence 
of salt. 
EXPERIMENTS. 
Two quarts of water were thoroughly mixed with 8 cubic inches 
of clay and placed in two milk bottles of quart size with flaring type 
of neck. I'wo tablespoonfuls of salt were mixed with one (A), the 
other (B) remaining a freshwater mixture. At the end of ten 
minutes the flocculated clay in A had settled 24 inches, and the upper 
21 inches of the mixture was clear enough to read fine print through 
neck of bottle. In ten minutes the sediment had settled 43 inches, 
the mixture being perfectly clear in the upper part. The fresh- 
water mixture showed no clearing during this interval. The settling 
was accompanied by constant upward currents of sediment all round 
the sides of bottle, starting from the contact of the flared and straight- 
sided part of the bottle. After the top of sediment had settled to the 
level of the straight-sided portion of bottle these upward currents on 
the sides ceased, and the surface of sediment at this stage was covered 
over by small fumarole-shaped mounds, 3 to 10 mm. in diameter, each 
with an opening at the summit the size of a pin-head or smaller. 
The B mixture showed no sign of clearing during this period. 
Eighteen hours after starting this experiment 2 inches of sediment 
had fallen to the bottom of A, and the liquid above was perfectly 
clear. The sediment still had the irregular miniature-mound covered 
surface noted above. No settling appeared to take place in B during 
this time. After forty hours, settling had nearly ceased in the saline 
mixture, leaving perfectly clear water above the 2 inches of sediment. 
The freshwater bottle showed its original turbidity throughout. 
Another freshwater mixture of this clay remained turbid after standing 
21 months. At the end of forty hours the saline mixture was thoroughly 
shaken and sedimentation started over again. The phenomenon noted 
above was repeated as already described, except that the process was 
slightly more rapid than in the first case. 
In order to test the effect of the shape of the containing vessel on 
the production of the ascending currents noted above around the sides 
1. M. Reade & P. Holland: ‘‘ Sands and Sediments,’’ Pt. I: Proc. Liver- 
pool Geol. Soc., vol. x, pp. 48-78, 1906. 
