^166 THE CANADIAN NATURALIST. [June, 



the veins, and varying in color from white to yellowish and flesh- 

 -red. The mineral has the chemical characters of flint or buhrstone, 

 •and like the latter presents numerous irregular cells, the walls of 

 which are sometimes incrusted with crystals of quartz, and in other 

 cases bear the impression of small cubes, perhaps of crystals of fluor- 

 spar, which have themselves disappeared. The relations of these 

 singular veins of silex show that it cannot be of sedimentary origin, 

 and it can scarcely be doubted that it is an aqueous deposit, and 

 results from a similar process to that which on a lesser scale gives 

 rise to agate and chalcedony in various rocks. (Geology of Canada, 

 page 41.) 



Trachytes. 



Under this head we shall describe a class of rocks which are 

 very abundant in Eastern Canada, and present a great variety of 

 aspects. There are many dykes in the vicinity of Montreal which 

 resemble some of the typical trachytic rocks of Auvergne and of 

 the Rhine ; while the rocks of the mountains of Brome and Sheffbrd 

 consist almost entirely of distinctly crystalline feldspar. These will 

 be described as granitoid trachytes, under which head may also be 

 included a somewhat similar rock from Yamaska Mountain. 



Brome and Shefford Mountains. — The trachytes of Brome 

 and Shefford occupy two considerable areas near to each other, 

 and, as already stated, are the easternmost of the eruptive masses 

 now under description. The larger area covers about twenty 

 square miles in Brome and the western part of the township of Shef- 

 ford. It consists of several rounded hills, of which the principal 

 are named Brome and Shefford Mountains, and rise boldly about 

 1,000 feet above the surrounding plain. The rock shows divisional 

 planes, giving it an aspect of stratification, and separates by other 

 joints into rectangular blocks. The second area includes about nine 

 square miles in the township of Shefford, to the northwest of the 

 last, and at the nearest point is only about two miles removed from 

 it. This is known as Shefford Mountain. 



The rocks of these two mountainous areas present but very 

 slight differences; being, so far as examined, everywhere made up 

 in great part of a crystalline feldspar, with small portions of brown- 

 ish-black mica, or of black hornblende, which are sometimes asso- 

 ciated. The proportion of these two minerals is never above a few 

 hundredths, and is often less than one hundredth. The other min- 



