1864.] T. STERRY HUNT ON LITHOLOGY. 171 



passing into bluish and grayish-white ; it has a feebly shining lus- 

 tre and is slightly translucent on the edges, with a compact or 

 finely granular texture, and an uneven sub-conchoidal fracture. 

 Before the blow-pipe it fuses with intumescence into a white 

 enamel. The rock in powder, is attacked even by acetic acid, which 

 removes 0.8 per cent of carbonate of lime, besides 1.5 per cent 

 of alumina and oxyd of iron ; the latter apparently derived from a 

 carbonate. Nitric acid dissolves a little more lime, oxydizes the 

 pyrites, and takes up, besides alumina and alkalies, a considerable 

 portion of manganese. This apparently exists in the form of sul- 

 phuret, since, while it is soluble in dilute nitric acid, the white por- 

 tions of the rock aflford no trace of manganese before the blow-pipe ; 

 although minute dark-colored grains, associated with the pyrites, 

 were found to give an intense manganese reaction. From the 

 residue after the action of the nitric acid, a solution of carbonate 

 of soda removed a portion of silica ; and the remainder, dried at 

 300° F., was free from iron and from manganese. Its analysis is 

 given under ix ; while that of the matters dissolved by nitric acid 

 and carbonate of soda from 100 parts of the rock, will be found 

 under ix A. 



A dyke of trachyte near to the last, and very similar to it in 

 appearance, was submitted to the action of nitric acid, but the in- 

 soluble residue was not treated by carbonate of soda. Its analysis 

 is given under x, while that of the soluble matters is to be found 

 under x A. A white trachyte from a dyke at Lachine, resembled 

 the preceding, but was somewhat earthy in its aspect, and effer- 

 vesced with nitric acid, which removed a portion of lime equal to 

 7.40 per cent of carbonate. On boiling the pulverized rock with 

 nitrate of ammonia, an amount of lime equal to 5.33 per cent of 

 carbonate was dissolved. An accident prevented the complete 

 determination of the alkalies in the feldspathic residue of this tra- 

 chyte ; and the soluble silica was not removed previous to the anal- 

 ysis, whose result is given under xi. The proportion of the 

 potash to the soda was however found to be, by weight, nearly as 

 two to three. The matters dissolved by nitric acid will be found 

 under xi A. 



Another dyke of trachyte from Lachine was concretionary, and 

 stained by infiltration ; the interior of the concretions was white 

 and earthy. The substances removed from 100 parts of the rock 

 by nitric acid and carbonate of soda, are given under b. A par- 



