43 
The following are analyses of two volcanic soils: 
Lime, Potash, Phesphorie acid, 
per cent. per cent. per cent. 
HP ULOM DeatMONt Nea 2 cata S.. on arate te a) = as ate 1.6 0. 226 0. 403 
SM BGO) ARTEL OIe eas tee = etc one Sa ame eee ae aes 2.6 O2160) 0, 304 
These soils are very fertile in spite of a slight depth of the arable 
stratum. Judging from these figures, the author is led to conclude, with 
M. P. de Gasparin, that phosphoric acid, rather than potash, is the 
measure of fertility of a soil. 
Soil of Limogne.—This soil is a rich alluvium, derived from the de- 
composition of all the rocks of Auvergne, the mud of ancient lakes, and 
even mineral-waters. The following are the results of three analyses of 
specimens of this soil taken from different localities: 
2 3 a3 
S ws 
ee 2 os 
Maes IAA: Rid = 
a D AS 
SUEDE Asse OE Sa LA SSE SS giclee SSSR aoe Pe a eee 16 
Physical analysis. - } Sand. SS 3s eh oo oes BOE SEER CIO Occ ab seeps aaet 42, 4. 69.7 
Cla wianGiene San G22 sao tbs ae eae ial oer ne os oe claete 55. 8 96. 14: 30 
100 100. 100. 00 
(PEROSPHOTIO RCI 2 2220s dpeee te ene eel aes ee i iieinian 0.296 | 0.329 416 
ARID OAS Hee apse te ee lee cla ee a oe aint Pletal r= ae 0.548 | 0.385 280 
g TMT Sek SAEs oe eS eS GR ee arom eases 9.970 | 8.893 3. 853 
Witio Resta. = ales oe eee gine ie in eens ee ae wenn 1.850} 0.005 0. 762 
Chemical analysis. ? Carbonate of lithia ........--------0---eseeeeeeeeeeneees 02085)? 08199). eee 
[OS ST Gre Tie ee ee RA Se eS Coe ee AS Sone eee a a a ay Be 15. 320 
CINGEIMN GE hose aoe fesedee ak estes sec eme nae eiel= te wel de aan O1069):|* OF06Ge) 25525 - 
Wan pO eo. See eee te pee eine Se dome made eeite cs eee sion W145i, W083" sca. eme 
ORR OLOE ENE soe orien ee a one ae Oe an Camie a etal See me ewe ae 0.310%)" (0.4534) -2 2s. 
The thickness of the arable layer of this soil, often exceeding. several 
meters, its looseness, as indicated by the physical analysis, &c., tend to 
make it very fertile; but if the proportion of phosphoric acid be con- 
sidered, it will be observed that it is three times as great as that which 
characterizes the best soils. The black color and exceptional fertility 
of this alluvium would lead one to classify it with garden-mold, and to 
suppose it very rich in humus. But its amount of carbon derived from 
organic matters is small, and many less fertile soils contain much more. 
The action of rocks in regard to fertility may be appreciated by ex- 
amining the composition of the subterranean waters coming from them, 
and which are more or less efficacious when employed in irrigation. 
Some waters in the department of Puy-de-Dome have the reputation of 
increasing the fertility of the soils upon which they are used, while 
others are known to be almost without effect. As might be predicted, 
the first come from voleanic. districts, the second from granitic. The 
following analyses confirm this supposition: 
Quantities in one liter. 
Phosphoric 
acid 
. q 
8 FI 3 s 
= = o ° 
nN | Ay nN 
FROM GRANITIC ROCKS. Milli- | Milli- | Milli- Milli- | MUilli- 
grams. | grams.| grams. | grams.| grams. 
40 
1 Traces} 2.7 2.0 | Traces. 
9 2.4 Rb 3.6 | Traces 
29 R5, 1.9 6.4 | Traces 
28.5 ph 8.2 13.5 | Traces 
33 Traces I area te 0. 873 
25 Traces} 1.2 4.9 1. 080 
17 Traces 1.5 5.0 0. 850 
