42 
COMPOSITION OF SIMPLE MINERALS. 
Railway passes. Still, I have seen good crops of rye growing there, though the soil may 
have derived a beneficial influence from the decomposition of the neighboring rocks com¬ 
posed of hornblende and sienite. Here is also a peculiar vegetation : the Ilex canadensis , 
and some other herbaceous plants, are only found here, and this is the only place where 
any thing like a pine grove has been planted by nature. For localities where serpentine 
prevails, see the Report of the Second Geological District. 
In this connection, it will be proper to state the composition of basalt and greenstone , 
although in New-York they do not form very extensive beds. 
Basalt. Greenstone. 
46.50 57.25 
16.75 25.50 
9.50 2.75 
2.25 . 
2.60 8.10 
20.12 3.50 
2.00 3.00 
97.72 100.10 
The composition, however, of these varieties of rock is extremely variable, but all are 
known to contain the alkalies and alkaline earths; and it is owing to this fact that the 
greenstone soils are remarkably fertile, so much so that they may often be employed to 
increase the fertility of less favored ones. 
§ 4. Character of granitic soils. 
Returning once more to the consideration of granitic soils, I remark, that they are too 
siliceous and porous when derived purely from granite. Position, however, alters their 
character ; for where they lie upon sloping surfaces, sand predominates ; but in the 
valleys, the fine alumine or clay of the felspar accumulates and forms an admixture of 
clay and sand, which is more favorable to the support of grass and grain. On reviewing 
the composition of the minerals which enter as elements in rocks, we find that the most 
abundant of them contain the proper proportions for a good soil. Silex rarely forms less 
than one-half; the remainder is made up of alumina (which is essential to the consistency 
of the soil), lime, potash, soda and iron, some containing more and some less of each 
respectively, the alkalies being the most essential, and rendering a soil rich, as it is 
termed, in proportion to their amount. In addition to the fact here stated, I may 
observe that the tendency to decompose is also increased in proportion to the percentage 
of the alkalies contained in the mineral: a rock of pure quartz is acted upon very 
slowly, while one in which felspar and mica exist crumbles rapidly. 
Silica,_ 
Alumina,- 
Lime,-— 
Magnesia,- 
Soda,- 
Iron and manganese, 
Water,- 
