﻿Yol. 64.] LAFEiENTIAN SISTEMIIT EASTERN CANADA. 139 



the direction of the bedding-plane which they follow and torn apart 

 by movements in this plane, the limestone-strata having, during 

 their upheaval, experienced somewhat extensive movements along 

 their bedding-planes. The dykes, after having followed the bedding- 

 planes for a certain distance, once more cut vertically across the 

 latter and so reach the surface. Such dykes when seen on limited 

 exposures of the bedded surface of the limestone, especially in 

 contorted districts, would usually present the appearance of inter- 

 stratified masses of amphibolite. 



This amphibolite has the regular allotriomorphic structure of a 

 completely recrystallized rock, and differs from any of the normal 

 igneous rocks. Under the microscope it is identical with an amphi- 

 bolite described by Dr. Teall, which was developed by the alteration 

 of a diabase-dyke where crossed by a line of shearing. In the case 

 of these Canadian dykes, however, the amphibolite is not confined 

 to that portion which has been clearly subjected to movement, but 

 forms the whole mass of the dyke. 



(c) Amphibolites which are identical in physical character and 

 in composition with those described under (b) are also produced hj 

 the metamorphic action exerted by the granite-batbyliths on the 

 limestones through which they cut. This is a remarkable fact, and 

 one which at first sight seems scarcely credible. It is, however, a 

 change which has undoubtedly taken place on a large scale. 



In addition to the amphibolites having originated in the three ways 

 above mentioned, it is highly probable, judging from their character 

 and mode of occurjence, that the amphibolite-bands associated with 

 the large gabbro- and diorite-masses — as, for instance, that running 

 in a north-easterly and south-westerly direction through the town- 

 ship of Wollaston, and that occurring in the south-eastern portion of 

 the township of Cardifi", thence crossing Chandos into Anstruther — 

 represent highly-altered basic volcanic ashes and lava-flows, con- 

 nected with vents represented by the gabbro-stocks. The latter of 

 these amphibolite-bands presents a great variation from place to 

 place, in the character of the constituent rock. While in some 

 places it is well banded, elsewhere it is streaked or presents an 

 appearance strongly resembling fiow-structure, with lighter-coloured 

 lath-like forms highly suggestive of felspar-phenocrysts thickly 

 scattered through it, while elsewhere the appearance suggests an 

 original amygdaloidal structure. The rock, however, is so com- 

 pletely recrystallized, that a microscopic examination does not yield 

 any conclusive evidence concerning its original character. 



YI. The Gabbros and the Nepheline-Syenites. 



In addition to the amphibolites which are of igneous origin, 

 there are several great intrusions of gabbro in the area. They are 

 composed of a dark basic gabbro, containing a considerable amount 

 of hornblende, which mineral, however, is often, and probabl; 

 always, of secondary origin. 



