206 ON THE CHEMISTRY OF METAMORPHIC ROCKS. 



masses, almost without any admixture, but at other times include 

 portions of pyroxene, which passes into hypersthene. Beds of 

 nearly pure pyroxenite are met with in this series, and others which 

 would be called hyperite and diabase. These anorthosite rocks 

 are frequently compact, but are more often granitoid in structure. 

 They are generally greyish, greenish, or bluish in colour, and be- 

 come white on the weathered surfaces. The opalescent labradorite- 

 rock of Labrador is a characteristic variety of these anorthosites ; 

 which often contain small portions of red garnet and brown mica, 

 and more rarely, epidote, and a little quartz. They are sometimes 

 slightly calcareous. Magnetic iron and ilmenite are often dissem- 

 inated in these rocks, and occasionally form masses or beds of 

 considerable size. These anorthosites constitute the predom- 

 inant part of the Labrador series, so far as yet examined. 

 They are however associated with beds of quartzose orthoclase 

 gneiss, which represent the first class of aluminous sediments, and 

 with crystalline limestones ; and they will probably be found, when 

 further studied, to offer a ^complete lithological series. These rocks 

 have been observed in several areas among the Laurentide Moun- 

 tains, from the coast of Labrador to Lake Huron, and are also met 

 with among the Laurentian rocks of the Adirondack Mountains ; of 

 which according to Emmons, they form the highest summits. 



In the third series, which we have referred to the Lower Silurian 

 age, the gneiss is sometimes granitoid, but less markedly so than 

 in the first; and it is much more frequently micaceous, often pass- 

 ing into micaceous schist, a common variety of which contains 

 disseminated a large quantity of chloritoid. Argillites abound, 

 and under the influence of metamorphism sometimes develop 

 crystalline orthoclase. At other times they are converted into a 

 soft micaceous mineral, and form a kind of mica-schist. Chias- 

 tolite and staurotide are never met with in the schists of this 

 series, at least in its northern portions, throughout Canada and 

 New England. The anorthosites of the Labrador series are repre- 

 sented by fine grained diorites, in which the feldspar varies from 

 albite to very basic varieties, which are sometimes associated with 

 an aluminous mineral allied to chlorite in composition. Chloritic 

 schists, freqently accompanied by epidote, abound in this series. 

 The great predominance of magnesia in the forms of dolomite, 

 magnesite, steatite and serpentine, is also characteristic of portions 

 of this series. The latter, which forms great beds (ophiolites), is 

 marked by the almost constant presence of small portions of the 

 oxides of chrome and nickel. These metals are also common in 



