38 DR. THOMAS STERRY HUNT ON THE 



layers of a white or colorless mineral. Some of the white layers are chiefly made up of 

 easily recognized stilbite, and the same mineral, in distinct tablets, forms the upper layer of 

 the whole deposit. There are also irregular seams of white running through the yellow 

 mineral." 



The greenish-yellow crystalline mineral was found to consist of laumontite, and the 

 other layers were mixtures of stilbite and laumontite, with some of which were found sphe- 

 rules of thomsonite. This, in other cavities, formed layers by itself, without admixtiire of 

 the other zeolites mentioned. The presence of these zeolites in cavities side by side with 

 other cavities which were entirely empty, is, according to the writers whom we have 

 quoted, apparently due to the fact that the former communicated with fissures which were 

 channels for the percolating waters that deposited the zeolites. Such fissures, filled up 

 with similar zeolites, were in many cases found leading to these cavities. 



§ *76. The eruptive rocks which break through the Trenton (Ordovician) limestone at 

 and near Montreal, in Canada, are of various ages and unlike composition. Some of these 

 are highl}' basic, and have been described as dolerites and diorites, while some have been 

 found to contain analcite, and others again much nephelite, and have been referred to 

 teschenite and nepheline-syenite. In some fine-grained amygdaloidal varieties of these 

 basic rocks, which have been designated dolerites, I long since described the occurrence of 

 heulandite, chabazite, analcite and natrolite, with quartz and epidote.'" These zeolites are 

 not abundant, but in certain of the basic doleritic rocks on Mount Royal I have found 

 remarkable A^ins of orthoclase with quartz and other minerals, which merit a notice in 

 this connection. Included in vertical dykes of these rocks, themselves cutting the horizontal 

 limestones which appear at the base of the mountain, are frequent granitic veins, some- 

 times twelve inches or more in breadth, parallel with the walls of the inclosing dyke, 

 often distinctly banded, and exhibiting a bilateral symmetry which, together with their 

 drusy structure, shews them to be endogenous. The most characteristic of these veins are 

 made up of white, coarsely-crystalline orthoclase with a little quartz which, in druses, 

 presents pyramidal forms. In some of the veins. Dr. Harrington has since detected, 

 besides orthoclase and quartz, nephelite, sodalite, cancrinite, hornblende, acmite, biotite 

 and magnetite. All of these minerals are seemingly secretions from the enclosing basic 

 exotic rock. 



§ VZ. The mineral secretions of the basic eruptive rocks may be conveniently grouped 

 under seven heads, as follows : — 



1. The aluminous silicates, including the zeolites properly so-called, to which we 

 append the related hydrous species, prehnite and chlorastrolite, and the associated 

 anhydrous species, orthoclase and epidote, which are common in the amygdaloidal rocks of 

 Lake Superior. To these we must add albite, axinite, tourmaline and sphene, observed by 

 Emerson, in 1882, in a diabase dyke in the trias at Deerfield, Massachusetts,"' and also the 

 various anhydrous aluminous silicates found with orthoclase in the veins on Mount 

 Hoyal, just described. 



2. The group of hydrous protoxyd-silicates, the bases of which are lime and alkalies, and 



'" Hunt, in Geologj' of Canada, 1803, pp. 441, 655 and 668 ; also Harrington, Report Geol. Survey of Canada, 

 1877-78, p. 43, G. 



" Emerson, Amer. Jour. Science, xxiv. pp. 195, 270 and 329. We reserve for another occaaion the discussion 

 of the paragenesis of the minerals of this locality, so carefully studied by Emerson. 



