30 GEOLOGY OF THE SECOND DISTRICT. 



blende is always in small masses ; and besides, the resemblance between the two minerals is 

 so great, that it always requires a careful inspection in order to distinguish them from each 

 other. This variety is generally spotted, the hornblende being collected into little clusters of 

 crystalline masses of a dark grey, which, appearing upon a lighter ground, gives it this aspect. 

 Small grams of garnet are common in tliis variety ; they are often obscure, and hence require 

 the assistance of a microscope to detect them. Garnet has not as yet been seen in crystals 

 much larger than a pigeon shot, and these are imperfect. 



Labrad&rite, Hornblende and Epidote, are also of frequent occurrence ; the latter generally 

 appears as a coating, which penetrates into the natural joints of the labradorite. It is known 

 by its pecuhar yellowisii green colour. It is not in sufficient quantity to give character to 

 the rock. 



Granular Labradorite and Mica, is a more common variety than the preceding ; the mass 

 is quite dark, and it lias more of a trappean appearance than any of the preceding varieties. 

 The mica occurs in small tufted radiating masses, and almost perfectly black. It has, too, 

 much of the spotted appearance of the hornblendic variety— a variety more abundant near 

 tlie junction of the hj'persthene rock with gneiss. 



Quartz, which is so abundant and constant in otlier primary rocks, is extremely rare in this. 

 Where it occurs, it is in seains, or thin irregular veins ; indicating, as it would seem, that it 

 does not form a constituent part of this rock. 



Magnetic oaride of iron is very generally diffused through the rock ; it appears in black 

 grains with a resinous lustre, and may be distinguished from the other dark colored minerals 

 by the magnet. Both garnet and iron are most abundant in tlie rock in the neighborhood of 

 the beds or veins of iron. In some instances, their presence seems to indicate proximity to 

 masses of iron. 



Jointed Structure. 



Hypersthene rock is traversed by a double system of joints, in consequence of which it 

 breaks into angular masses or forms. Those joints, or divisional seams, run S. 5° W. and 

 N. 85° E. I have found a variation in this direction, amounting to from 5° to 10°, when 

 observed at different places. Near the suminit of mountains, tliick beds or lamina of the rock 

 sepai-ate from the mass in a direction almost parallel to the slope or face of the mountain ; 

 appearing precisely like stratification, and might be taken for it, did we not know that the rock 

 is unstratified, and that such an arrangement would not be in accordance to the usual course 

 of the layers composing a stratified mass. 



By the operation of various causes in these high regions, blocks became detached entirely 

 from the main rock, and are finally perfectly insulated like ordinary boulders, and appear as 

 if they had been brought from a distance, and left on the perfectly bare rock on which they 

 rest ; and this might perhaps he the theory which some geologists would propose to account 

 for their insulated position ; but being precisely similar to the mass on which they rest, it is 

 more rational to consider them weather-detached masses which in ancient times once com- 

 posed a part of the very rock on which they now repose. 



