Williams — Geology of Arisaig-Antigonish District. 249 



is thus presupposed between the Listmore and the Ardness 

 formations. 



Summary of the Carboniferous deposits. — The three forma- 

 tions of Carboniferous age are much alike in their general char- 

 acters. Although exhibiting minor Hexiug and faulting, the 

 strata have not suffered great disturbances and overlap the 

 great fault zone which affected the older formations. They 

 generally dip with gentle gradients away from the rocks repre- 

 senting the older land. The many highly inclined contacts and 

 the unsorted, breccia nature of the basal conglomerate, partic- 

 ularly along the scarps of the plateau consisting of Upper 

 Cambrian rocks, suggest deposition of material near its source 

 in previous troughs of erosion. The McAra's Brook conglom- 

 erates probably represent a phase of continental sedimentation 

 which was later characterized by swampy conditions or, at any 

 rate, non-oxidizing conditions, which favored the deposition of 

 gray sandstone and beds of oil-shale and impure coal. Shallow 

 marine or littoral conditions followed, culminating in the lay- 

 ing down of the basal Ardness limestone. Shallower waters 

 again prevailed, and in isolated pans gypsum deposits collected 

 as a result of excessive evaporation. As the Appalachian rev- 

 olution began to affect the area, continental conditions finally 

 superseded the littoral and continued not only during the depo- 

 sition of the upper beds of the Ardness formation and the whole 

 thickness of the Listmore formation, but according to the work 

 of Fletcher lasted through the formation of the coal measures 

 and the deposition of the Permian in the vicinity of Pictou 

 and westward. The Windsor submergence was evidently the 

 last of marine conditions for northern Nova Scotia. 



Igneous Geology. 



A number of eruptive and irruptive rocks are associated with 

 the Upper Cambrian formations of the Arisaig-Antigonish dis- 

 trict. The largest individual intrusion is that of fine-grained 

 pink granite north of James River station. This is in the 

 form of a stock, and as seen in surface exposures is dense and 

 evidently represents conditions not far removed from the con- 

 tact with the former cover. East of Malignant Cove, what 

 appears to be an irregular monzonite stock is exposed along the 

 shore. A neck of rhyolite forms the center of the Sugar Loaf 

 Hill south of Malignant Cove, and rhyolite exposures in the 

 vicinity indicate that erosion has laid bare considerable masses 

 of an eruptive rock which had never quite reached the surface. 

 The rhyolite grades into quartz porphyry containing large phe- 

 nocrysts of orthoclase feldspar. The irregular porphyry bodies 

 evidently represent intrusions similar to those of the rhyolite 

 but more deeply eroded. 



