SHELL. 
tion, on account of its seldom affording per- 
manent or injurious lodgment to snow; for, when 
any considerable degree of wind prevails, no 
sooner does the snow come within the wall, than 
it is elevated by the whirling blast or current 
which sweeps the enclosure, and is carried over 
the wall and thrown out; and even when no 
wind blows, and when the snow lies and accumu- 
lates steadily where it falls, the sheep within the 
stell always keep above it, and have been known, 
in a case of heavy and long-continued fall, even 
to raise themselves upon the accumulating de- 
posit to the very level of the wall. Some per- 
sons, however, prefer winter-stells in the form of 
the letter T, or in that of the letter H, or in that 
of the letter 8S, or in that of various lines and 
curvatures expressly adapted to the special con- 
figuration of the ground; and others have at- 
tempted, with more or less success, to combine 
the properties of winter-stell and summer-stell 
by means of a complex form of projecting en- 
closures and intermediate recesses,—the former 
for retreat from snow-storms, and the latter for 
shelter from hurricanes. But summer-stells are 
wanted in different situations from the winter 
ones, and do best within or near the brow of 
hills, in spots to which the flocks most frequently 
retreat from the fury of the blast, and may con- 
sist only of a semicircle or two transverse walls 
on a declivity, or of three walls diverging from a 
common centre on the top of a knoll, or of a 
single line of wall on the wing of a cliff or pre- 
cipitous escarpment. See the articles Foup and 
SHELTER. 
SHEEP-WALK. See Pasture. 
SHELL. A hard, close, cubical envelope, 
either natural or artificial. The word is used in 
very many and widely different senses; but it 
concerns a. naturalist or an agriculturist prin- 
cipally in the sense of the hard, calcareous coat 
of birds’ eggs and of the bodies of molluscs and 
crustaceans. A shell, in this sense, is a mineral 
substance, with some intermixture of animal 
matter ; and, when properly used, acts readily and 
richly as a fertilizer of the soil. Egg shells consist 
principally of carbonate of lime with some mag- 
nesia, but comprise about one per cent. of phos- 
phate of lime and magnesia, and from two to 
four per cent. of animal matter ; the shells of mol- 
luses have a compact texture, an enamelled sur- 
face, and sometimes splendid variegation of tint 
and outline, and consist almost entirely of car- 
bonate of lime, with layers of coagulated albu- 
men, or with a soft animal substance similar to 
gelatine; and the shells of crustaceans contain a 
large proportion of carbonate of lime, a consider- 
able proportion of phosphate of lime, and a.quan- 
tity of cartilaginous matter similar to coagulated 
albumen. 
the tides or embedded in the bottom of bays and 
estuaries, form both an abundant and an excellent 
manure. See the articles Sanp and Sueni-Sanp. 
Large quantities of entire or partially broken 
The comminuted shells deposited by | 
SHELTER. 203 
shells, whether obtained from natural deposits 
or accumulated artificially, may be prepared for 
prompt manurial action either by pulverization 
or by calcination; but though, in the latter way, 
they fall readily to powder, they are liable to 
sustain a wasteful loss of their animal matter. 
See the articles OystER and AnimAL Manurzs. 
SHELL-LAC. See Lac and Coccus. 
SHELL-SAND. A natural mixture of sea- 
sand and comminuted shells. See the article 
Sanp. “The shell-sand of our coasts is often 
obtained in the state of a fine powder; and in 
that form it acts better than in a coarser form, 
and the same weight goes farther. But none of it 
is so fine as the powder to which slaked lime falls. 
It has, therefore, occurred to many that it might 
be rendered more valuable by a partial burning. 
The shell-sand which is collected on our coasts 
contains a variable proportion of sea-sand. This 
sometimes is as little as 5 or 10, but at other 
times it amounts to as much as 50 or 60 per 
cent. of its whole weight. This variation will, 
of course, affect its value as a manure in what- | 
ever state it is applied. In consequence of this 
admixture of sand among the shells, it will un- 
avoidably happen, during the burning of them, 
that in those parts of the fire or kiln where the 
heat is greatest, a portion of the sand and lime 
will occasionally melt together, and form a sili- 
cate of lime. So much of the lime as has thus 
been converted into silicate, will, of course, be 
less immediate in its action upon the soil, al- 
though it will be by no means without an ulti- 
mate good effect. When mixed with the soil, it 
will by degrees be reconverted into carbonate, and 
will at the same time liberate a portion of silica in 
that soluble state in which, in some soils, it may 
possibly promote the growth of the corn crop 
and strengthen the straw. This roasting or 
burning of the shell-sand has been tried with 
success in ‘Cornwall. By burning it has been 
found to become so brittle as easily to be reduced 
to a fine powder; and in this powdery state, it 
has produced on several farms, a marked increase 
in the crops of roots and corn. This was of 
course to be expected, especially on cold un- 
drained lands, and such as were naturally poor 
in lime. The native shell-sand would have pro- 
duced the same effects in a less marked degree. 
Ordinary lime shells, newly fallen or slacked, 
would -have produced a fully equal effect. This 
method of burning the shell-sand, therefore, 
though it greatly inproves it, does not give it 
virtues which other lime does not possess.” [Re- 
port of the Agricultural Chemistry Association 
of Scotland. ] 
SHELTER. The sheltering of sheep is treated 
in the articles SHeep, SuHerp-Stetn, and Foun; 
the sheltering of cattle is noticed in the article 
Frrpine or AnrmAts ; and the sheltering of fields 
and pastures and tracts of country is disposed of 
in the articles Puantation, Encirosurn, Fence, 
Wat, and Hepner. In this place, therefore, we 
