GKANITIC IRRUPTIONS OF VARIOUS AGES. 191 



veins similar to those caused by shrinkage on cooling in granite of admit- 

 tedly eruptive origin. 5. It contains fragments of slates and schists im- 

 bedded in it. He also states that the evidence afforded by the study of thin 

 slices confirms the conclusion arrived at by the stratigraphical evidence, and 

 gives a summary of the microscopic evidence.* 



The very able and precise descriptions by Barroisf of the various granitic 

 irruptions which have affected Brittany at different ages from the pre-Cam- 

 brian up to the Carboniferous show beyond question that not only in 

 Archean times, but at various subsequent periods were the conditions 

 which characterize the Archean of Canada reproduced. He describes par- 

 ticularly the "granite gneissique," demonstrates its irruptive origin, and 

 notes not only the contact metamorphism, but also the injection of these 

 rocks " en filonnets minces et repetes " within the encasing schists. His 

 descriptions and figures of repeated injections of granite within the schists, 

 so as to produce an alternation simulating bedding, closely corresponds with 

 the contact phenomena described by the writer as observed between the 

 Laurentian and Keewatin on the Lake of the Woods, the interpretation of 

 which is entirely in accord with that of Barrois, though questioned by Pro- 

 fessor A. Winchell.J It would appear that just as in Hunter's island, north- 

 west of Lake Superior, we have two generations of Laurentian rocks from a 

 sub-crustal magma, so in Brittany there have been several generations of 

 similar rocks breaking through the overlying crust, extending in time as 

 late as the Carboniferous. 



In Norway Kjerulf $ places the " Gebanderte granit, oder gneisgranit " 

 with the eruptive rocks, and states that in numberless places such rocks 

 break through the strata of the gruudgebirges, and also, indeed, through the 

 Bergenschiefer in which Reusch has since found Silurian fossils. |j In the 

 greater part of Norway he says (translated freely) ^[ — 



" What was formerly recognized as gneiss must on the map he now designated as 

 granite. The reason why the older observei-s assume it to be gneiss is the granular 

 banded structure, which we must distinguish from the appearance of bedding. On 

 older maps are shown also other great regions in which the dip and strike of the beds 

 is given, an attribute which they do not in reality possess; and the reason for this 

 lies in the confounding of foliation with bedding. * * * The rock, according to 

 the old conception, is granite when no bedding occurs in it. The modern view, 

 which had already been announced by Delesse, says : ' En realite c'est [le gneiss granit] 

 seulement une variete du granit, qui est veinee et qui parait avoir ete genee dans sa 

 cristallisation.' " ** 



*Geol. Mag., loc. cit. 



fBull. Soc. Geol. de France, 3me Serie, t. XIV, 1886, pp. 655-898. 



j Geol. Survey of Minnesota, Fifteenth Annual Report, 1886, p. 201, \ 5. 



§ Die Geologie des Sud. und Mit. Norwegen, Bonn, 1880, p. 237. 



|| Fossilien Fiihrenden Schiefer von Bergen, Leipsig, 1883. 



If Op. cit. p. 282. 



** Delesse, Etudes sur le Metamorphism, 1861. 



