34 THE CANADIAN NATURALIST. [March 



Rocks composed chiefly of labradorite or a related feldspar 

 greatly predominate in the Labrador series, but these, at least in 

 the area near Montreal, which is the one best known, are inter- 

 stratified with beds of a kind of diabase, in which dark green 

 pyroxene prevails, with crystalline limestone similar in mineral- 

 ogical character to that of the Laurentian system, and more rarely 

 with quartzites and thin beds of orthoclase gneiss. I have more 

 than once insisted upon the rarity of free quartz, and the general 

 basic character of the rocks of this series, an observation with 

 which I am credited in Dana's Manual of Geology (p. 139), 

 where it seems to be applied to the whole of the rocks there classed 

 as Azoic, including the Laurentian, Labrador and Huronian 

 systems. It is, in fact, remarkable that the silicated rocks of the 

 latter two consist chiefly of labradorites, diorites and diabases; 

 gneissic and granitic rocks being exceedingly rare among them, 

 though quartzites abound in the Huronian. In the Laurentian 

 system, on the contrary, though basic silicated rocks are not want- 

 ing, orthoclase gneisses, often granitoid in structure, and abounding 

 in quartz, predominate. 



The anorthosite rocks of the Labrador series present great 

 variations in texture, being sometimes coarsely granitoid, and at 

 other times finely granular. They not unfrequently assume the 

 banded structure of gneiss, lines of pyroxene, hypersthene, garnet, 

 titanic iron-ore or mica marking the planes of stratafication. 

 Probably three-fourths of the anorthosites of this series, in Canada, 

 whether examined in place, or in the boulders which abound in 

 the St Lawrence Valley, consist of pure or nearly pure feldspar 

 rocks, in which the proportion of foreign minerals will not exceed 

 five hundredths. Hence we have come to designate them by the 

 name of labradorite rock. The colors of this rock are very 

 generally some shade of blue, from bluish -black or violet to bluish- 

 gray, smoky-gray or lavender, more rarely purplish passing into 

 flesh-red, greenish-blue, and occasionally greenish or bluish-white. 

 The weathered surfaces of these labradorite rocks are opaque white. 

 The anorthosites, which occupy a considerable area in the Adi- 

 rondack region, as described by Emmons in his report on the 

 Geology of the Northern District of New York, and as seen by 

 me in hand-specimens, closely resemble the rocks of the Labrador 

 series in Canada. 



In all of these localities the coarse or granitoid varieties often 

 hold large crystalline cleavable masses, generally poly synthetic 



