42 COMPOSITION OK SIMPLE MINERALS. 



Raflwa] passi s. Still, I have Been good crops of rye growing there, though 1 1 » « - soil may 

 have derived b beneficial influence from the decomposition of the neighboring rocks com- 

 posed of hornblende and Bienite. Here is also a peculiar vegetation: tbe Bex canadensis} 

 and some other herbaceous plants, are onlj found here, and tliis i> the onlj 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 tins connection, it will be propel t" Btate the composition of basalt and greenstone, 

 although in New-York they do not form verj extensive beds. 



w.t. Greenstone. 



Silica 46.50 57.25 



Alumina, 16.75 25.50 



Lime, 9.50 2.75 



Magnesia 2.25 



Soda 2.60 8.10 



Iron and manganese. 20.12 3.50 



Water, 2.00 3.00 



97.72 100.10 



The composition, however, of these varieties of rock is extremely variable, hut all arc 

 known to contain the alkalies and alkaline earths ; and it is owing to this fact thai 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 snrfacea, sand predominates : but in the 

 valleys, tbe line aliimine 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 



tb. nposition of the minerals which enter as (dements in rock-, we find that the most 



abundant of them contain the proper proportions for a good soil. Silex rarely tonus less 

 than one-half: the remainder is made up of alumina (which is essential to the consistency 

 of the soil), lime, potash, soda ami 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 

 rve 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 

 6lowly, while one in which felspar and mica exist crumbles rapidly. 



