54 ROYAL SOCIETY OF CANADA 



island is not thus constituted. The trappean rocks are found along the 

 north side of the island through its entire extent, rising in precipitous 

 cliffs from 300 to 400 feet in height. 



We come now to consider the several agencies, hypogenic or epigenic, 

 by which the various features already described have been determined. 

 The hypogenic influences may be first reviewed. 



Hypogene Agencies. 



Deformation and Igneous Action. — Changes in the nature of sedi- 

 ments, such as from conglomerates to sandstones or shales or from either 

 of these to limestones, are in themselves proofs of changes of level co- 

 €sxtensive with the spread of the strata exhibiting them. The order of 

 succession also is often indicative of cycles of change, involving the re^ 

 currence of slight upward and downward movements, but, except as such 

 changes determine rocks of different powers of resistance to wear, they 

 rarely find eipression in the existing features of the surface. It is not 

 necessary nor possible to consider them fully here. On the other hand 

 there have been through the ages deformatory movements of more signi- 

 ficant character and the influence of which in the determination of 

 modern physiographic features can be clearly recognized. It is not al- 

 ways easy or even possible to say at just what time these effects of eleva- 

 tion or depression, folding or faulting, took place, but the following 

 summary is based on such information as seems now to be available. 



1. Pre-Cambrian. — That the ridges which constitute the Southern 

 Highlands were uplifted prior to the opening of the Cambrian era seems 

 altogether probable, being indicated both by the structure of the Pre- 

 ('ambrian system itself and the relations thereto of the overlying Cam- 

 brian sediments. Not only are these unconformable, showing movements 

 prior to their deposition, but they are shallow water deposits, and as 

 such must have been derived from land areas which were not far distant. 

 TherGj is reason to believe that such land existed to the east and south, 

 beyond the present limits of Nova Scotia, but the nature of the conglo- 

 merates in the lower members of the Cambrian would seem to point to 

 the southern hills of New Brunswick as the more probable source of 

 supply. The discordance of both dip and strike between the lower and 

 upper divisions of the Pre-Cambrian rocks in these hills are a further 

 indication of early earth movements in the region, while, thirdly, the 

 vast accumulations of volcanic matter which characterized the so-called 

 *' Huronian " division, attaining in places a thickness of a mile and a 

 half, point clearly to similar changes of level. Finally the region is in- 

 tersected by numerous faults, and though some of these, such as that 

 occupied by the valley of the St. John river below the mouth of the 



