1864.] T. STERRT HUNT ON LITHOLOGY. 183 



which, in its general aspoct, greatly resembles that of Yamaska just 

 described, except that it is rather more feldspathic. The finer- 

 grained varieties are grayish in color, and exhibit a mixture of 

 grains and small crystals of feldspar, with hornblende, brown mica, 

 and magnetite. Frequently however the rock is much coarser- 

 grained, consisting of feldspar grains, with slender prisms of black 

 hornblende, often half an inch long and tenth of an inch broad, 

 and numerous small crystals of amber-colored sphene. In this 

 aggregate there are imbedded cleavable masses of the feldspar, 

 sometinies an inch long by half an inch in breadth. At the south- 

 ern foot of the mountain, large blocks of the coarse-grained diorite 

 are found in a state of disintegration, affording detached crystals of 

 feldspar with rounded angles, and weathered externally to an opaque 

 white, from a partial decomposition. Near to the base of the moun- 

 tain, a coarse-grained variety of the dioriti; encloses small but dis- 

 tinct crystals of br )wn mica; and a fine-grained micaceous variety, 

 containing sphene, occurs near the summit. 



The feldspar, in all the specimens examined from thi-^ mountain, 

 appears to be uniform in character. Its color is white, rarely 

 greenish or grayish; it has a vitreous lustre, inclining to pearly, 

 and it is somewhat translucent. The cleavages of this feldspar 

 reseuible those of oligoclase, with which species it also agrees in 

 specific gravity and chemical composition. The macled forms, so 

 common in the crystals of triclinic feldspars, have not however 

 been detected in the specimens from this locality. A fragment of 

 a crystal uave a density of 2.631, and another portion in powder, 

 2.659. The results of its analysis are given under xxii and xxiil. 



XX. XXI. XXII. xxiir. XXIV. 



Silica 46.90 47.00 62.05 62 . 10 58.30 



Al"^"i"^ 31. 10^32^5 22.60 ....) ^^^^ 



Peioxyd of iron 1.35' .75 .... » 



Lime 16-07 15.90 3.96 3.69 5.43 



Magnesia '65 .... .... .... .91 



Potash ^S 1.80 2.74 



Soda 1.77 7.95 6.73 



Volatile 1.00 .80 .50 



99.42 99.91 99.32 



Bklcetl. — The specimens which have been examined from this 

 mountain onsist of a kind of micaceous diorite. The feldspar, 

 which so far predominates as to give a light gray color to the mass, 



