Ix PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



mechanically dispersed throughout their substance; and the re- 

 searches of Daubree, Deville, and others have proved how some of 

 the silicated minerals composing the lavas retain for a length of 

 time, and up to the moment of their solidification, large quantities 

 of water, thus showing that it would remain a constituent of simi- 

 lar rocks until they are relieved from superincumbent pressure by 

 actually making their appearance at the surface, when they would 

 be subjected only to the ordinary weight of the atmosphere. 



Among the foremost in applying the researches of chemical geo- 

 logy to the elucidation of the structure of a vast tract equal in 

 extent to many of our European kingdoms. Sir William Logan and 

 Mr. Sterry Hunt have in Canada arrived at remarkable conclu- 

 sions. The descriptive catalogue prepared by them for their un- 

 rivalled collection of the rock-substances contributed by the Survey 

 to the last International Exhibition, and the voluminous Eeport pub- 

 lished in 1863, are fraught with facts and suggestions of great 

 value. Among the eruptive rocks a large proportion occur vdth a 

 character so like those of their European congeners, and under cir- 

 cumstances so similar, that no doubt is felt by the writers as to their 

 origin. The felspathic rocks described by them under the name of 

 trachyte occur in large masses in the mountains of Brome and Shef- 

 ford, and, as dykes of a clearly intrusive character, at Chambly and 

 near Montreal. No uncertainty appears to exist as to the similar 

 origin of the diorites of Yamaska, Mount Johnson, and Beloeil and 

 Rigaud Mountains. More interesting are the dolerites, part of 

 them composed chiefly of black crystalline augite, sometimes almost 

 to the exclusion of every other mineral. These rocks, especially 

 abundant in the county of Grenville, are referred to three (hfferent 

 periods of eruption — one during the Silurian epoch, one before it, 

 and another after it. The newest of them is, however, said to be 

 traversed by, and therefore to be more ancient than, the " trachytes" 

 of Montreal and Chambly. The dolerites are largely found, both in 

 dykes and masses, in the mountains of MontarviUe, E,ougemont, and 

 Mount Eoyal. Occasionally, as in the former of these localities, 

 varieties different in colour and texture are arranged in bands, 

 " whose varying thickness and curving lines suggest the notion that 

 they ha 70 been produced by the flow and the partial commingling 

 of two semifluid masses." The dolerites are thus attributed to a 

 much earlier period than has been allowed to them by observers 

 in European regions. That of Montarville is noticeable for the 

 large size of its imbedded crystals of augite, and for its great pro- 

 portion of olivine in yellowish-brown rounded crystalline masses, 

 from one-tenth to half an inch in diameter. Its felspar is stated 

 to have nearly the composition of labradorite. The similar rock 

 from the other localities contains also olivine in places, and is di- 

 stinctly seen to break through the Lower Silurian strata ; and when 

 it is alleged that fragments of that mineral and of augite are 

 found in the dolomitic conglomerates near Montreal, we have 

 what appears to be decided evidence of the intrusion of these 

 rocks before the close of the Silurian period. This conglomerate, 



