37 
EEVIEWS. 
Carte Agronomi que des Environs de Paris. By M. Delesse. 
A " Carte Afjronomique des Environs de Paris " has been published by 
M. Delesse. We need not say that a map by the able engineer of mines and 
professor of geology at the Ecole Normale is a good one. M. Delesse is one 
of those men who never do anything otherwise tlian well. Although the 
Tegetable soil is only of slight thickness its importance is very great, and 
many savants, at the head of whom is M. De Caumont, have attempted to 
represent its variable composition by special maps called " Cartes Agro- 
nomiques," M. Delesse has lately laid before the French Society of 
Agriculture one of these maps for the environs of Paris. Such labours 
are not without considerable difficulties in their execution. The soils 
require detailed and minute examinations, and their characters sometimes 
change completely in contiguous districts ; on tlie other hand, the elements 
remain nearly always the same, and vary more in their proportions than 
in their nature. This uniformity of materials causes the greatest difficulty 
in denoting the mineralogical composition, changing sometimes in an in- 
sensible and gradual manner; and thus, whilst, on the one hand, the 
different vegetable soils are not separated by exact limits, on the other, 
the mineralogical composition is very complex. It is hence scarcely 
possible to figure them by tints, as oiie would do a geological rock. The 
notation adopted by M. Delesae is in this manner: — The soil richest in 
humus is indicated by fine blue diagonal hatching ; the sand, gravel, and 
stony debris forming the residue of lajvigation, by red parallel signs ; and 
the clay, marl, humus, and particles strained off' in Itevigation, by vertical 
blue signs, and so on. To render sensible to the eye the proportions of 
the principal substances over the extent of the maps, these signs have been 
disposed methodically in small squares. 
The details given by M. Delesse on the conditions and manner of oc- 
currence, and quantities in diflierent places, are highly instructive. The 
soils he finds always contain clay, sand, and ordinarily stony debris. The 
humus is also found in a constant manner, and is essentially characteristic 
of a vegetable soil. It is especially very abundant in vaileys and in all 
depressions of the soil, even when these cavities are seated on tops and 
sides of hills. Particularly it is concentrated in the bottom of damp 
valleys, and where the soil is saturated with water. 
Limestone is found in variable proportions, but its disposition is subject 
to definite laws. It is wanting generally on the heights. It is wanting 
also in the soils on the terraces bordering the Seine and the Marne. It is 
absent even at the head of the valley of the Bievre. The calcareous region 
includes the thalwegs, the depressions on the plateaux, the flanks of the 
hills, and particularly the bottom of the valleys. 
The proportion of carbonic acid in the vegetable soil is, on the plateaux, 
nil, or reduced to mere traces. It is only when a very thick diluvial 
deposit reposes on a calcareous subsoil that it can attain to a fevr 
hundredths. On descending a hillside, the carbonic acid is very scanty at 
the upper part, but augments progressively with the declivity, offering at 
times various alternations. The same occurs in descending a valley ; in 
that of the Bievre, for example, carbonic acid is wanting in all the elevated 
portion ; it then augments as the valley descends until it finally attains 
10 per cent. On the shores of the Seine and the Marne, it sometimes 
exceeds 25 per cent. The residue of Isevigation is essentially formed of 
sands coming from the Fontainebleau beds, from flint, gravel, and the 
