AGRICULTURAL GEOLOGY. 11 



At the north, however, this substance existing in but a small pro- 

 portion in the hypersthene rock, has but little influence upon the 

 uality of the soil ; besides, being mixed largely with labradorite, 

 1 rhich contains both lime and alumina, the soil formed therefrom 

 lay be considered as good for grains and grass. Quartz or silex, 

 )0, is extremely scarce in this rock ; and hence there is no ex- 

 ess of sand in it, as there is usually in a pure granitic soil, 

 [ypersthcne, upon the whole, may be considered as rather a rare 

 liiu ral in New-York. It is found in gneiss in Johnsburgh, but 

 I siuh small quantities that it has no influence upon the soil. 



Serpentine is another primary rock, disposed to crumble into 



111. It is one in which magnesia is the characteristic element. 



consists of 



Serpentine. 



Silica, 40.08 42.69 



Magnesia, 41.40 40.00 



Water, 15.67 16.45 



Protoxide of iron, 2.70 1.00 



99.85 Shepard. 100.14 Vanuxem. 



•Serpentine may be known by its softness, and yellowish green 

 I lor. It is easily cut by a knife, or easily impressed, and it is 

 jlvvays found softer upon the outside than upon a fresh fracture ; 

 1'e color, too, is much paler on the weathered surface. 



In foreign treatises on agricultural geology, serpentine is set 

 j|Wn with those rocks which make a poor soil. Thus, Johnson 

 feaks of the soil at the Lizard in Cornwall, as being far from fer- 

 Ic, and so retentive of water as to form swamps and marshes; 

 cd even when drained, it rarely produces good grass, or average 

 dps of corn. It is the opinion of the same distinguished writer, 

 tit the barrenness is due to the small quantity of lime contained 

 i the soil ; serpentine, as will be seen from the above analysis, 

 t|ing destitute of this element. In New-York, and part of New- 

 lli gland, it would appear that the serpentine exists under different 

 iilitions. Thus, in St. Lawrence, Jefferson, Essex and Warren 

 canties, it is intermixed with lime, and the lime disintegrates 

 ri)re rapidly than the serpentine ; the soil, therefore, must con- 

 tn a sufficient quantity of lime. However this may be, there is 

 avays a luxuriant growth of vegetables about these beds. The 

 s pentine hills of New-England are not so productive as those of 



