42 
possibility of obtaining nitrogen from any external source other than 
the atmosphere, they produce sufficient herbage for pasturage of large 
herds of cattle throughout six months of the year, and contain a higher 
percentage of nitrogen than could by any means be supplied by the 
excreta of the cattle pastured there. f 
It might be objected that the nitrogen could be supplied by atmos- 
pheric ammonia produced at lower altitudes and carried up by the 
moisture that goes to form clouds; but this objection will not hold in 
view of the fact that the soil of Theix, found at an elevation of only 
1,500 feet, contains nearly as much nitrogen as the-soil of Besse. The 
other instances cited support this fact, and while we by no means dis- 
pute the agency of ulmic compounds in the appropriation of atmospheric 
nitrogen by the soil, and must acknowledge the vaiue of Mons. Trachot’s 
results, showing in some cases an increase of nitrogen with increase of 
carbon, we cannot fully agree with Lim in concluding from these results 
that ‘* the amount of nitrogen contained in soils is in direct proportion 
to the quantity of carbon in the ulmic compounds they contain.” 
PHOSPHORIC ACID AS AN INDICATOR OF THE FERTILITY OF SOILS.— 
Mons. P. Truchot, in another paper, has discussed this idea in an exceed- 
ingly interesting manner, giving results of a series of analyses of soils 
of Auvergne, made with especial reference to it. Basing his estimations 
upon the fact that the three mineral ingredients of soils resulting from 
the decomposition of rocks which are of most value as fertilizers are 
lime, phosphorie acid, and potash, he obtained the results given below. 
Granitic soils—The granites of Puy-de-D6me are almost entirely 
deficient in lime, and are poor in phosphorie acid, potash alone being 
present in notable quantity. The following are the results of estima- 
tions made upon the more or less decomposed friable rocks which form 
the subsoi] of the cultivated soil, after having formed the soil itself: 
F Phospho- 
Lime. Potash. Se enrisiis 
Per cent. | Per cent.| Per cent. 
1. Granite from Bourgnon, (Canton de St. Dier) ............------------ | 0. 040 0. 160 0. 015 
2. Granite from Trezioux, (Canton de St. Dier)....-...-....------.----- 0. 099 0. 332 0. 048 
SA AST TN Rae pT TUT TN ETT R TTT a alia eo ea Saati yee re Traces .. 0.345 Traces. 
4. Granite from Theix, (Canton de Clermont) ............------.------- Traces... 0. 371 0. 037 
5. Gneiss from Chéry, (Canton de Sauxillauges) ........-...--...------- Traces .- 0.115 Traces. 
The soils resulting from the decomposition of these granites, or simi- 
lar granitic rocks, are only slightly fertile, and require lime and phos- 
phatic manures. The mean of analyses of twenty-three of these soils 
gives: Lime, 0.039; potash, 0.210; phosphoric acid, 0.058. 
Volcanic soils—It is quite different with volcanic soils, whether 
formed from basaltic rocks or modern lavas. The decomposition of 
rocks containing pyroxene and labradorite furnishes lime, so that such 
soils, athough classified with the preceding as sandy, do not generally 
require an addition of lime. They contain a tolerably large amount of 
potash, and especially a large proportion of phosphoric acid. 
The foilowing are the quantities of phosphoric acid in several vol- 
canic rocks: 
1. Dette, irom Pny-fe-Dome. 2. 2... -6 <nnee == or ¥.n 2 es cil Ses es ss 
Oe Demitee tron Buy-de-DOmM6 2... ss core ne Lace cates nce Beer cies ce 2:01 
SiDtaehyuos from Mont! Doré): 222 2cs bh AR eo ee seo RS Le 
4; Rasalinemeosis,; (Pont des:Matix) - 0.2. $2 oo 2.6 ..a2- te obsess 2 
5.) Pozzolang: fram, Gravenoil ,.-« 4. -iaiekehs.ec.a ma Bech kien Mewes brs ~lom pape hee 
6. luava, from Gravenoitend=:\s 2 ssc caer pees e3- oh cco be hae ote etope => m oo oe 
7. Lava, from Gravenoir; parfly decomposed -.:... ~~ / 2. .-sepenens~ toons eeeeee 0.742 
