﻿Origin of the Grenvillc and Hastings Series. 307 



foliation or owing to subseciuent movements, when the 

 rock was in a more or less plastic condition, often assume 

 long ribbon-like forms. That great movements have 

 taken place in the whole series during or after this 

 invasion is shown by the complicated twisting of these 

 darker bands and masses into all manner of curious and 

 intricate forms, as well as in the frequent rolling out 

 of great blocks of the amphibolite, after having been 

 penetrated in all directions by small pegmatite veins, 

 resulting in masses of a dark basic gneissoid rock, filled 

 with strings, bunches, separated fragments or grains of 

 quartz or feldspar, giving to the mass a pseudo-conglo- 

 meratic appearance. 



There can be but little doubt that the various c^neissic 

 rocks, constituting the more acid part of the series, are of 

 truly igneous origin ; and there is no evidence whatever 

 of their having ever formed part of a sedimentary series. 



The true character of the more basic members is more 

 uncertain, but they are probably closely related to the 

 pyroxene granulites of Saxony, and doubtless represent 

 either differentiation-products of the original magma, or 

 basic intrusions whose structural relations and characters 

 have been largely masked by the great movements which 

 have taken place in the whole series at a later date. 



The Grenville Series differs from the Fundamental 

 Gneiss in that it contains certain rocks whose composition 

 marks them as highly altered sediments. These rocks 

 are chiefly limestones, with which are associated certain 

 peculiar gneisses, rich in sillimanite and garnet, having a 

 composition approaching ordinary shale or slate, or else 

 very rich in quartz and passing into quartzite, having 

 thus the composition of sandstone. These rocks, as has 

 been shown in one of the papers before referred to, 

 usually occur in close association with one another, 

 and are quite different in composition from any igneous 

 rocks hitherto described. They are considered as con- 



