206 ON THE GEOLOGY AND PETROGRAPHY OP BATHURST, N.S.W., 



rocks of that region can be resolved into two great divisions. The 

 lower composed of rocks which but for their foliation are regarded 

 as of plutonic igneous origin. Resting on these is a mass of 

 stratiform rocks, partly detrital, partly volcanic. These latter, or 

 upper series, were certainly not laid down on the lower. The old 

 floor on which they were deposited has disappeared ; and again, 

 Dr. Lawson points out that the lower series could not have been 

 the crust from which the detritus for forming the upper rocks was 

 derived. 



" There is but one way of reconciling these statements. It is a 

 simple conception, and one well in accordance with established 

 geological truth, that certain portions of the earth's crust upon which 

 strata are accumulating may sink gradually. Now, that portion 

 of it upon which the upper archean was accumulating, to a thick- 

 ness of several miles, may be conceived to have been depressed, 

 either by reason of the superincumbent weight or from other 

 causes, till it came within a zone of a sort of fusion compatible 

 with the conditions of such depths. This fusion gives us the 

 magma which is implied in the conception of the laurentian gneisses, 

 granites, and syenites, being of plutonic igneous origin."* 



Vancouver Island furnishes another example that may throw 

 some light on the origin of the Bathurst granite. Dr. Gr. M. 

 Dawson has described the relations of granites to triassic beds in 

 Vancouver and the adjacent coasts. Triassic beds are frequently 

 found in contact with, or resting upon, granite rocks. They were 

 not, however, deposited on a granitic floor, as the granites are 

 evidently of a later date. " The circumstances attending the line 

 of junction of the granites with the rocks of the Vancouver 

 (triassic) series have been carefully examined at a great number 

 of points. The granites near this line are usually charged with 

 innumerable darker fragments of the Vancouver series, which, 

 when in the immediate vicinity of the parent rock, are angular 

 and clearly marked, but at a greater distance become rounded and 

 blurred in outline, and might then be mistaken for concretionary 



* Congres Geologique International, Londres, 1889 ; pp. 75, 76. 



