SEA SAND. 
47 
(which are therefore detained), but smooth compared to the 
larger stones (which therefore roll to the bottom). When 
rain falls upon a heap of sand and gravel, the sand goes to the 
bottom whilst the gravel remains, because the rain is able to 
wash away the finer grains, but does not stir the heavier 
stones. On the Northumberland coast, after a strong wind off 
shore, I have seen a plain swept almost bare of sand, leaving 
the gravel in coarse ripples a yard or so apart. 
In comparing the fineness of two different samples of sand, 
it is not necessary to actually measure the grains. We have 
found it convenient to divide the sand into grades of fineness 
by means of a series of graduated sieves. These are made (in 
Stonegate and elsewhere) from wire gauze, so as to have 
io, 20, 30, or some other number of holes to the linear inch. 
20 holes to the inch does not imply that particles yrr inch in 
diameter will just slip through. The wires have some thick¬ 
ness, and such particles would not get through. Perhaps the 
most useful sizes are 30, 60, and 90 to the inch. But the 
complete set w r e have used runs from 10 to 90 (omitting 70). 
Using these, a sample of sand may be separated into some 10 
different grades. (I have allowed for the lack of a 70 sieve 
by splitting the 60 to 80 grade of sand into two arbitrary 
portions). 
A sample of sand has been passed through the whole series 
of sieves, and the quantities rejected by each sieve have been 
transferred to upright measuring jars so that their volumes 
may be compared. 
Rejected by 
10 20 
30 
40 
50 
60 
70 80 
90 
— 
Passed by.. 
10 
20 
30 
40 
50 
60 70 
80 
90 
Volume 
6 
+ 
ol 
O • 
0 
12 1 
21' 
8- 
2' 
very 
still 
little 
less 
If the 40 to 50 grade is the largest portion, then the 
adjacent grades 30 to 40 and 50 to 60 are the next commonest, 
and the two extreme grades (rejected by 10, and passing 90) 
are the rarest. This sounds common sense. It is like saying 
that most of the sand has a diameter not very different from 
the average diameter. But there is more in this orderly 
