10 QUARTERLY JOURNAL. 



Together with a variable proportion of oxide of manganese am 



fluoric acid. 



Hornblende, which often replaces mica in the granites, is usual] 



a dark green substance, and extremely tough in the mass. It 



commonly crystaline, and more or less fibrous. It differs essen 



tially from the micas and felspar, in containing larger proportioil 



of lime. It consists of 



Hornblende. 



Silica, 42.24 



Alumina, 13 .92 



Lime, 12 . 24 



Magnesia, 13.74 



Protoxide of iron, , 14 . 59 



Oxide of manganese, . 33 



Fluoric acid, 1.50 



98.56 



All these substances are termed silicates ; the silica uniting wi' 



each of the principal elements as an acid, and forming therel 



silicates of alumina, potash, magnesia, and iron. In the northe 



as well as the southern highlands, pyroxene or augife enters large( 



into the constitution of the primary rocks. Its composition dd 



not differ materially, so far as its effects upon a soil is concerna 



from that of hornblende ; thus, 



Pyroxene. 



Light colored. Dark colored. 



Silica, 55.32 54.08 ■( 



Lime, 27.01 23.47 p 



Magnesia, 16.99 11.49 



Protoxide of iron, 2.16 10.02 



Alumina, 0.28 0.14 



Manganese, 1.59 0.61 J^i 



103.35 99.81 Rose. 



To the same family belongs the hypersfhene, which gives na 

 to the rock forming the highest grounds of Essex, namely, /I 

 persthene rock. This substance contains less lime than hornblenjBli 

 or augite, and hence is less favorable as an element of soil ; in fa* 

 it is remarked, that where it exists in sufficient abundance to ini' 

 ence the nature of the soil, it is quite barren. It is composed ol 



HYrERSTHENB. Bl 



Silica, 51.35 



Lime 1.84 



Magnesia, 11.09 



Protoxide of iron, 33.92 



Water, 0.50 



P). 



98.70 



i 



