37 



EEVIEWS. 



Carte Agronomique des Environs de Paris. By M. Delesse. 



A " Carte Agronomique 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 Normal e is a good one. M. Delesse is one 

 of those men who never do anything otherwise than well. Although the 

 vegetable 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 

 arc not without considerable difficulties in their execution. The soils 

 require detailed and minute examinations, and their characters sometimes 

 ehange completely in contiguous districts ; on the other hand, the elements 

 remain nearly always the same, and vary more in their proportions than 

 i ii 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 one would do a geological rock. The 

 notation adopted by M. Delesse 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 lsevigation, by red parallel signs ; and 

 the clay, marl, humus, and particles strained off in lsevigation, 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, ami quantities in different 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 valle} r s 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 few 

 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 Some and the Marne, it sometimes 

 exceeds 25 per cent. The residue of lsevigation is essentially formed of 

 sands coining from the Fontainebleau beds, from Hint, gravel, and the 



