Petrographical Relations of Laurent tan Limestones. 5 



line limestones or marbles everywhere characteristic of 

 the G-renville Series, which have been described at length 

 by Dr. T. Sterry Hunt 1 and various other writers. The 

 source of the nietamorphism which has produced this 

 recrystallization — whether due to the heat from the 

 igneous intrusions, to the dynamic action which has un- 

 doubtedly taken place, possibly accompanying these 

 intrusions, or to other causes altogether different — is a 

 subject which does not closely concern the present 

 arguments. Away from the intrusions before described, 

 the limestones are comparatively pure, though they some- 

 times contain bands of very dark hornblendic rocks or 

 amphibolites, but approaching the igneous rocks, they are 

 found to contain little rounded grains of pyroxene and 

 other lime-rich minerals, and in many cases to pass into 

 banded, basic rocks which warrant the field name of 

 pyroxene gneiss. These become darker in color yet nearer 

 the granite, and are still found to contain intercalated 

 with them and with layers of limestone, bands of amphi- 

 bolites, which have a harder or more granitic look than 

 the pyroxene gneisses, but are otherwise quite similar in 

 appearance. They are somewhat more sharply defined 

 from the marbles than are the pyroxene gneisses, the 

 transition from one to the other being often quite abrupt. 

 The whole series is cut by dykes, veins, or stringers of the 

 granite which anastomose through it in a remarkable way, 

 and the resulting appearance is most complicated. Nearer 

 still to the invading mass these bands become more and 

 more broken and indefinite, the number and size of the 

 granite dykes increase ; and at last comes the state of 

 affairs where the dark rocks occur as inclusions in the 

 granite. In the south-western portion of the large central 

 batholite shown in the accompanying map, these inclusions 

 are very numerous indeed. They vary in size from a few 



1. "Geology and Mineralogy of the Lanrentian Limestones," Geol. Surv. Can., 

 Rep't. of Progress, 1863-66, p. 181, et seq. 



