i 88i.j Miniature Physical Geology . 713 
grains of sand, when they come to rest in the pool, form a 
slope of very constant angle, which by a number of mea- 
surements I found to be 40° for coarse sand and 34° for fine 
sand, the average angle being 36V’ — (“ Nature,” March, 
1878.) I have repeated these measurements on miniature 
deltas on the Cape Flats, and found similar angles. One of 
my notes on these miniature deltas is to the following effect : 
— “ The delta seems to push further and further out into 
the miniature sea, until at last it has formed a long low spit. 
If now a little freshet comes down, the stream overflows to 
some extent its own delta, and ere long forms at one side of 
its original course a fresh channel, which leads to the sea by 
a shorter course.” I was not aware at the time that I wrote 
this note that a similar action occurs on a large scale. In 
Mr. Belt’s interesting “ Naturalist in Nicaragua,” however, 
I find the following passage : — “ If the Colorado were not 
to be interfered with by man, it would, in the course of ages, 
carry down great quantities of mud, sand, and trunks of 
trees, and gradually form sand-banks at its mouth, pushing 
out the delta further and further at this point, until it was 
greatly in advance of the rest of the coast ; the river would 
then break through again by some nearer channel, and the 
Colorado would be silted up, as the Lower San Juan is being 
at present. The numerous half-filled-up channels and lagoons 
throughout the delta show the various courses the river has 
at different times taken.” 
X. Miniature Drift Currents. 
Below the chalk cliffs between Ramsgate and Margate 
there are, at low water, long pools, in which I have some- 
times watched with interest the formation of miniature drift 
currents. “ I remember watching with interest such a cur- 
rent, which flowed between tiny chalk cliffs through the 
straits which separated two miniature seas ; the most in- 
structive point being that the finer grains of sand at the 
bottom of the straits, where the water was some 7 inches 
deep, were rolling over each other in such a manner as to 
prove the existence of an under current setting in the opposite 
direction to that in which the surface current was flowing.” 
— (“Nature.”) On a subsequent occasion I was able, by 
means of more or less loaded bladders, to see one near the 
top drift in one direction, another near the bottom drift in 
the opposite direction, while the third, sunk half-way, re- 
mained nearly stationary. At the leeward end of this pool 
there was a miniature delta, upon which the waves gradually 
VOL. III. (THIRD SERIES). 3 A 
