OEIGIN OF CEYSTALLINE KOCKS. 39 



of which pectolite may be taken as the type. These species are sometimes wrongly spoken 

 of as belonging to the class of zeolites. As an aj)peudnge to this group, we note the 

 hydrous borosilicate of lime, datolite, frequently found in these rocks. Mention shovild 

 here also be made of the anhydrous protoxyd-silicates, hornblende and acmite, in the 

 feldspathic veins of Moiant Royal. "We have already called attention to the occurrence of 

 hornblende and pyroxene in granitic veins under other conditions (§ 5*7). 



3. Quartz in its various crystalline and crypto-crystalline forms, as rock-crystal, 

 amethyst, chalcedony, agate and jaspery varieties, is found both alone and associated with 

 the minerals of the preceding groups. Hyalite of very recent origin has also been 

 observed by Emerson at Deerfield. 



4. The oxyds, magnetite and^hematite, are frequent in the zeolite-bearing rocks of Nova 

 Scotia, where both of these species form veins in amygdaloid, and where magnetite 

 moreover occurs in drusy cavities with quartz, laumontite and calcite. Hematite, in the 

 form of plates of specular ore, is also foiind there in veins with laumontite, and manganese 

 oxyd is sometimes associated with these iron-oxyds. Small crystals of hematite on 

 prehnite, with a little manganese oxyd, have been observed by Emerson at the Deerfield 

 locality, as also cuprite on datolite, and malachite on prehnite. In similar associations he, 

 moreover, found small portions of various sulphids, such as chalcopyrite, pyrite, sphalerite 

 and galenite. 



5. The presence of native copper, and occasionally of native silver, associated with the 

 various silicates already named, should also be noticed. The former metal is common 

 to the zeolitic rocks of Lake Superior and Nova Scotia. 



6. Mention should here be made of the saponite often found in amygdaloidal rocks, 

 which, in its pu.rer form, is a hydrous silicate of magnesia, with but little alumina or iron- 

 oxyd. Matters, apparently of this class fill, or more frequently line, amygdaloidal cavities 

 which are filled with other species. This magnesian hydrous silicate is perhaps distinct in 

 origin from the delessite or iron-chlorite which is a frequent constituent of many basic 

 rocks, such as the melaphyres of Lake Superior, and is probably not a secretion but a 

 residual product of the transformation of the rock. 



*7. Calcite in various forms is a common species in the rocks in question, and 

 fluorite and barytine may also be mentioned as accidental minerals therein. 



It is principally with the first two classes of minerals, the zeolitic group, with 

 its appendages, and the pectolitic group that we have to do. These two, as is well known, 

 though chiefly found in the eruptive rocks already noticed, are not confined to them. 

 Some species of zeolites occur occasionally in veins in gneiss and other crystalline rocks, 

 and even in limestones and other sedimentary deposits. These occurrences are the more 

 readily understood when we consider that the same minerals have been recently formed 

 by the action of thermal waters in various localities, and are even generated in sub-marine 

 ooze. Many of the species of these two groups have also been formed artificially in the 

 chemist's laboratory. 



§ 78. It is our present purpose to consider, first, the zeolitic, and secondly, the pectolitic 

 group, both as regards their chemical composition and their relations to various anhydrous 

 silicates. "We shall then proceed to notice the action of water at high temperatures on glass 

 and similar bodies, in giving rise to various crystalline species, including quartz. In this 

 connection will also be discussed some facts relating to the chemistry of the alkaline 



