116 W. A. Richardson—The Relative Age of Concretions. 
1. A flocculent precipitate, obtained by the addition of ammonia 
water to a solution of an aluminium salt, had a very low angle of 
repose, but settled in still water along the flatter slopes. The slightest 
movement of the water, such as that due to a gentle tapping of the 
vessel, caused immediate settlement of the precipitate to a level 
surface. 
2. Fine silver sand had a greater angle of repose, and also required 
a much stronger water-movement to level it. 
3. There was no tendency for either of these to adhere to the 
plasticene surface. When the deposit accumulated along the slope 
in still water the layer as might be expected was thicker at the base. 
Snow may be frequently seen to heap up over objects. But it does 
so permanently only when partial melting and refreezing have 
welded it into something like a continuous sheet. A slight breeze 
is sufficient to blow dry, powdery snow from elevated objects, and 
it then settles intc drifts, the shape of which is determined chiefly 
by wind-eddies and the protection afforded by surrounding objects. 
Beds 
ee ee 
ti. 7Eontem porany :+.° 5, Ze SS 
“i heous Concrehon}. ..:.-' ae Subsequent 
——= Concre he Cds 
art ewe 
ZrO). 9 0, 
ea AS 
(c) 
Fic. 1.—(A) Type of sedimentation around a contemporaneous object ; 
lamine thinner than object. (B) Similar to (A), but laminsw thicker 
than object. (C) Vertical loading on contemporaneous concretion pro- 
ducing ‘‘catenary’’ bedding. (D) Conformity of bedding planes to 
subsequent concretion, produced by displacement during growth. 
In any case the density and viscosity of such a medium as water 
would, when in motion, be more effective than air in bringing loose 
material to a gravitational surface. Ample confirmation of this is 
afforded by the examination of stream beds, pools, and shore margins. 
Boulders and other objects stand clear even of a sandy deposit, for, 
