1864.] t. sterry hunt on lithology. 173 



Phonolite. 

 Associated with the numerous trachytic dykes at Lachine 

 is one of the phonolite ah-eady referred to. It is brittle and some- 

 what schistose, breaking into angular fragments, and appears to 

 consist of a reddish fawn-colored base, in which are disseminated 

 greenish-white rounded masses, often grouped, and apparently 

 concretionary in their structure. These greenish portions are some- 

 times half an inch or more in diameter, and cover from one third 

 to one half of the surfaces. They are not very distinctly seen un- 

 less the rock is moistened. The hardness of the different portions 

 does not greatly vary, and is nearly that of apatite. The specific 

 gravity is very low, being only 2-414. The mass contains small 

 cavities filled with carbonate of lime, which is rarely stained pur- 

 ple : it is also found in small films in the joints. The rock is gran- 

 ular in its fracture, without lustre, and is feebly translucent at 

 the edges. When pulverized, and treated with nitric acid of spe- 

 cific gravity 1.25, a slight effervescence ensues, with abundant red 

 fumes. The mass grows warm, and gelatinizes ; and on washing 

 out the acid solution, and treating the insoluble portion with a 

 solution of caustic soda, a white granular residue remains. These 

 reactions are obtained both with the fawn-colored and the srreenish 

 portions, but the amount of insoluble matter is greater from the 

 last. The rock is but slightly hygroscopic : a portion of it in pow- 

 der lost only 0.2 per cent by a prolonged exposure to 212° ¥., 

 but 7.10 per cent at a red heat. 



For the quantitative analysis, the method already indicated was 

 followed. It was found that while a dilute solution of caustic soda 

 removed all of the gelatinous silica separated by the acid, it took 

 up only a trace of alumina ; leaving a feldspathic residue which 

 was no longer attacked by nitric acid. The silica was separated 

 from the alkaline liquid, and the acid solution was found to con- 

 tain, besides alumina and soda, a little potash, some lime, magne- 

 sia, and iron, and traces of manganese. The greater part of the 

 lime is evidently present as carbonate ; for when a portion of the 

 pulverized phonolite, which gave to nitric acid lime equal to 4.36 

 per cent of carbonate, was boiled with a solution of nitrate of am- 

 monia, there were dissolved 3.87 per cent of carbonate of lime; 

 besides which there was a separation of a considerable amount of 

 oxyd from the decomposed carbonate of iron. From this reaction, 

 and from the entire absence of sulphur, which was carefully sought 



