114 HOW CROPS FEED. 
has a greasy feel, and in composition is a hydrous silicate 
of magnesia. See analysis. 
Serpentine is a tough but soft massive mineral, in color 
usually of some shade of green. It forms immense beds 
in New England, New York, Pennsylvania, ete. It is also 
a hydrous silicate of magnesia. See analysis. 
Chrysolite is a silicate of magnesia and iron, which 
is found abundantly in lavas and basaltic rocks. It is a 
hard, glassy mineral, usually of an olive or brown-green 
color. See analysis below. 
TALC. SERPENTINE. ._ CHRYSOLITE. 
Bristol, Conn. New Haven, Conn. Bolton, Mass. 
Dr. Lummis. G. J. Brush. G. J. Brush. 
Silica, 64.00 44.05 40.94 
Alumina, oe sae 0.27 
Protoxide of iron, 4.%5 2.53 4 37 
Magnesia, 27.47 39.24 50.84 
Lime, — —— 1.2% 
Water, 4.30 13.49 3.28 
Zeolites.—Under this general name mineralogists are 
in the habit of including a number of minerals which have 
recently acquired considerable agricultural interest, since 
they represent certain compounds which we have strong 
reasons to believe are formed in and greatly influence the 
properties of soils. They are hydrous silicates of alum- 
ina or lime, and alkali, and are remarkable for the ease 
with which they undergo decomposition under the influ- 
ence of weak acids. We give here the names and compo- 
sition of the most common zeolites. Their special signif: 
icance will come under notice hereafter. We may add 
that while they all occur in white or red crystallizations, 
often of great beauty, they likewise exist in a state of 
division so minute that the eye cannot recognize them, 
and thus form a large share of certain rocks, which, by 
their disintegration, give origin to very fertile soils 
