ON THE CULTIVATION OF INDIGENOUS OPIUM. 325 
Bat cultivators in general here being in a great measure ignorant of 
chemistry, recognise only four sorts of earth, which they call by the 
names of cold earth, warm earth, light earth, and hard or stony earih. 
They comprehend under the name of warm earths all those which are 
easily penetrated by rain water, and do not retain it long ; that become 
hot by the prolonged action of the sun, and retain heat a considerable 
time. 
They give the name of cold earths to those which are slowly warmed 
by the action of the sun on account of the presence of water which they 
hold for a long time. Under this class may be ranged marly and 
clayey earths. 
I purpose speaking in another place of light earths and hard earths. 
But there is another classification of soil, much more rational, esta- 
blished by the learned and distinguished geologist, M. Thirria. 
He divides them into five classes, according to their mineralogical 
constitution — viz. : 
1st. Hard earths. 
2nd. Light earths. 
3rd. Poor earths. 
4th. Ferruginous earths. 
5th. Magnesian earths. 
Hard or stony earths, he saya, are compact, difficult to work, and 
are not easily penetrated by water. They are either yellowish, red, or 
of a greyish black. These earths, which are marly or clayey, are fertile 
when alumina is not in too great a proportion, but when it predominates 
the earth is too long in a damp state, the water not being able to escape 
easily, and the roots of vegetables decay. 
Light earths are friable and easily worked ; their colour is generally 
greyish or yellowish. They are sandy, calcareous, or marly. They owe 
their friability either to the silica or to the lime which predominates in 
their constituent parts when they are sandy or calcareous, or to the 
heaps of small calcareous stones which divide them when marly. 
They are very productive when the proportions of silica or of lime 
are not so strong as to prevent their absorbing a sufficient quantity of 
water for vegetation, or when the amount is abundant of small cal- 
careous stones, in which case these stones have the advantage of 
admitting the introduction of water to the soil, and of warming it by 
transmitting atmospheric heat better than the surrounding earth. 
The earths called poor are those which, being sandy or calcareous, 
contain a great deal of silica or lime. Their colour is generally 
whitish or yellowish grey ; they are unfruitful, because they cannot 
retain enough water to transmit to vegetables the quantity necessary for 
their growth. 
Ferruginous earths are of a red colour, more or less deep, and are 
always clayey. They are in general barren, because the oxide of iron 
with which they are charged contains often a small quantity of pro- 
