72 Geological Society. 
the north of that steppe, over a vast area, in broad valleys, on slopes 
and plateaux, and at all levels to the height of 400 feet ; also on rocks 
of all ages, even overlapping the southern skirts of the great north- 
ern drift. It invariably constitutes the surface-soil, and is composed 
of black particles mixed with grains of sand, the former being so 
fine as to rise into the air even under the pressure of a horse’s feet 
on the turf which covers it. 
One of the marked features of all the alluvia of Russia charac- 
terises also the Tchornoi Zem. Wherever it occurs on plateaux or 
slopes, it is cut into by the ravines, called “ avrachs” or “ baltas,” 
produced in the first instance by fissures formed during droughts, 
and widened as well as deepened subsequently by debacles arising 
from the melting of the thick falls of snow. 
This black earth constitutes the finest soil in Russia, both for 
grass and wheat, and after yielding many crops in succession, it re- 
quires only a year or two of fallow to regain its fertility ; the pea- 
sants, moreover, have prejudices against the use of manures, and 
Mr. Murchison believes that these feelings are strengthened by the 
natural productiveness of the soil. 
2. Chemical Composition.— An analysis of aportionof the Tchornoi 
Zem, made by Mr. R. Phillips, Chemist to the Museum of Economic 
Geology, yielded in 100 parts, 69:8 silica, 13°5 alumina, 1°6 lime, 
7° oxide of iron, 64 vegetable matter, and traces of humic acid, 
sulphuric and chlorine*. The black earth does not therefore differ, 
Mr. Murchison observes, in the composition of its solid contents 
from many of the red or brown soils of England. 
3. Origin of the Tchornot Zem.—In speculations on the origin of 
this deposit, the author dissents entirely from the opinion that it is 
due to decayed forests, as it never contains, even when exposed to 
the depth of 20 feet, any traces of. trees, roots, or vegetable fibres, 
not connected with the existing vegetation. On the contrary, he 
believes it to be a subaqueous accumulation, but he objects to the 
views entertained by those geologists who place it, as respects its 
mode of production, on a parallel with the loess of the Rhine, or 
* Since the paper was read the author has been favoured with an ana- 
lysis by M. Payen, the celebrated French agricultural chemist. The follow- 
ing statement is a translation of part of M. Payen’s communication :— 
100 parts 6°95 combustible organic matter. Alumina... 5:04 
Magical i 93°05 incombustible Soluble in Oxide of iron 5°62 
matter. boiling hy- 13°75 GING secede 0°82 
drochloric Bot Magnesia . 0°98 
acid. | Alkaline 1-21 
Chlorides } 
Insoluble Silica....... 71°56 
in boiling -_— Alumina. 6°36 
hydrochlo- thay Lime traces  — 
ric acid. Magnesia. 0:24 
The combustible organic matter indicated the presence, in 100 parts of the 
original earth, of water 4°81, azote 2-45, or together 7-26. The volume of 
the azote, M. Payen states, is remarkable. 
