CLATTING. 
perennial-rooted weed of the chalky and gravelly 
pastures of Britain. Its stem is about two feet 
high ; its leaves are greyish-green ; and its flowers 
are small and bluish-violet-coloured, and bloom 
from June till October. It has cordial and as- 
tringent qualities, whether fresh or dried; and 
is much esteemed, by many persons, for medicinal 
purposes and for flavouring wine.—A number of 
other species of Salvia are sometimes popularly 
called clary. See the articles Sacr and Satvra. 
CLASSIFICATION. See Borany and Sorts. 
CLATTING. The removing of a portion of 
the wool from the tails and udders of pregnant 
ewes a little before their lambing. The practice 
is effected by throwing the ewes, and is very 
useful, as a preventive of the mischievous cohe- 
sion of the wool from the effects of purging. 
CLAUSENA. A small genus of evergreen, 
tropical fruit-trees, of thé orange tribe. The 
five-leaved species, Clausena pentaphylla, formerly 
called Limonia pentaphylla, was introduced to 
our hothouses from India in 1800, It grows in 
India, to the height of 20 or 25 feet; its flowers 
are white, and bloom from June till August ; and 
its fruit is smooth, roundish, red, and about the 
size of a cherry, and is eaten by the common 
people. 
CLAY. Any kind of earthy matter which is 
characterized by the presence of alumina. See 
the articles Arumina and ArerLuacnous Haru. 
Clays, in a geological respect, are of very various 
age and character, and are found in great abun- 
dance, composing strata of more or less importance 
and distinctiveness, from nearly the lowest fos- 
siliferous beds up to the most recent alluvium. 
See the article Gronoey. Even surface clays, or 
clays lying near the surface, are very diversified 
as to both their origin and their mineral consti- 
tution. Some yellow clay, such as abounds in 
many parts of Denmark, is supposed to consist 
of the altered felspar, the unaltered mica, the 
pulverized quartz, and the recombined magnetic 
and titanic oxides, of decomposed granite. Most 
blue clays consist of decomposed syenite and 
greenstone, and do not contain any mica. Many 
clays have been formed by the disintegration of 
porphyry, and are easily distinguishable into 
thin quartzose, felspathic, and peculiarly alumin- 
ous constituents. ‘“ The analysis of the porcelain 
clays,” says liebig, “ proves that the felspars 
from which they were formed have not reached 
their utmost limit of disintegration, for they still 
contain potash. The porcelain clays are those 
which are refractory in the fire, and do not melt 
when exposed to the strongest heat of our fur- 
naces, The difficult fusibility of the porcelain 
clays depends upon their proportion of the alka- 
line bases, potash, soda, lime, magnesia, and pro- 
toxide of iron. When we compare the other 
kinds of clay with the porcelain clays, we find 
ber.—The vervain species, Salvia verbenacea, is a 
CLAY. 811 
the most kinds of rocks, those occurring in arable 
land, and those in the beds of clay interspersed 
with the layers of brown and mineral coal, con- 
tract when exposed to heat, and become vitrified 
in a strong fire. Loam also melts in a similar 
manner. When the oxides of iron are not pre- 
sent in the clays, their fusibility is in direct pro- 
portion to the amount of their alkaline ingre- 
dients. Clays arising from the disintegration of 
the potash felspars, are free from lime; those 
formed from Labrador spar—the principal com- 
ponent of basalt and lava—contain lime and soda. 
“The limestones containing much clay are pro- 
portionally the richest in alkaline ingredients. 
The marls and stones used for cement belong to 
this class of minerals. They differ from other 
limestones by possessing the property, after burn- 
ing, of hardening, when in contact with water. 
During the burning of marl and of many other 
natural cements, the constituents of the clay and 
lime act chemically upon each other, giving rise 
to anhydrous apophyllite, or an analogous com- 
pound of silicate of potash and silicate of lime, 
which, being brought in contact with water, 
forces the latter into chemical combination in a 
similar manner to burnt gypsum, and crystallizes 
along with it. When a fragment of chalk is 
moistened with a solution of silicate of potash, 
the latter forms a new compound on the surface, 
and this becomes hard and stony. The lime of 
the chalk takes the place of potash in the sili- 
cate of potash, and a certain quantity of potash 
is set at liberty in the form of a carbonate. 
“The preceding remarks prove very clearly 
that arable land has had its origin in the chemi- 
cal and mechanical actions exerted upon rocks 
and minerals rich in alkalies and alkaline earths, 
by which means their coherence has been gra- 
dually destroyed. It is scarcely necessary to fur- 
nish any further proofs that all clays, whether 
they be pure or mixed with other minerals, so as 
to form soils, suffer progressive and continued 
chatlzes. 
a soluble form to the alkalies and alkaline bases, 
by the combined action of water and of carbonic 
acid. This gives rise to the formation of soluble 
silicates, or, if these are decomposed by the car- 
bonic acid, to the hydrate of silica, which, being 
in its peculiar soluble condition, may be taken up 
by the roots of plants.” 
A clayey subsoil requires peculiar, operose, and 
expensive management, but will be discussed in 
the article on Dratninea; and clayey soils, of dif- 
ferent characters, require peculiar husbandry 
and considerable nicety of treatment, but will 
be discussed in the articles on Soin and Ro- 
TATION. Some varieties of clay surface are al- 
most totally barren; and others are the most 
exuberantly fertile within the British dominions. 
See the articles Carsr and Barren Soins. The 
worth or worthlessness of clayey land is depend- 
that the infusible clays, or clays poor in potash, | ent, in many instances, on the porosity or the 
are of rare occurrence. The clays diffused through | retentiveness of the subsoil, but, in more, upon 
These changes consist in the giving of - 
