218 Williams — Geology of Arisaig-Antigonish District. 



formation, has shown from Ostracoderm fishes obtained from 

 the lower strata that the deposits may he correlated directly with 

 the lower Old Red Sandstone of Europe. In origin the Knoy- 

 dart formation is evidently continental and probably originated 

 in large measure along the estuary of a Lower Devonian river. 



Mississippian deposits. — Mississippian sedimentation is rep- 

 resented in the Arisaig-Antigonish district by the McAra's 

 Brook and Ardness formations. The former consists of red 

 conglomerates, sandstones, and sandy shales, and on the east 

 of the area includes considerable thickness of micaceous gray 

 sandstone and oil-shale. Remains of Catamites and fern-like 

 impressions have been found in the oil-shale. Near the top 

 the sandstone is limy and is apparently conformably overlain 

 by the basal limestone of the Ardness formation. 



The limestone which forms the lowest stratum of the Ard- 

 ness formation is about 20 feet in thickness, and is succeeded 

 by red sandstone and sandy shales, with some similar inter- 

 bedded deposits of gray or greenish gray color. Along the 

 south of the district, particularly in the valley occupied by the 

 Intercolonial Railway, gypsum deposits probably 200 feet thick 

 succeed about 200 feet of red sandstone and shale which rest 

 upon the basal limestone. In the gray beds, particularly in 

 those exposed along Northumberland Strait, fossil plants and 

 carbonized wood occur in small amounts. The horizon-mark- 

 ing fossils are brachiopods obtained from the basal limestone 

 exposed west of McAra's Brook. These are : Productus doub- 

 leti Beede, very common ; P. dawsoni Beede ; Pugnax sp. 

 undet. ; Martinia glabra (Martin) ; and Beeclieria davidsoni 

 Hall and Clarke, rare. The limestone is thus shown on faunal 

 evidence to be the same as that occurring at Windsor in the 

 Windsor series. On the basis of the age determination thus 

 made and the apparent conformability of the McAra's Brook 

 and Ardness formations, they are both considered to be of 

 Mississippian age. 



? Pennsylvanian deposits. — Westward along the Northum- 

 berland Strait the Ardness formation is overlain by strata con- 

 sisting of red and gray sandstone and sandy shale. Fletcher 

 has termed these rocks the Millstone Grit formation ; to avoid 

 possible confusion with other areas in Nova Scotia, also thought 

 to be equivalent to the so-called Millstone Grit, the present 

 writer has distinguished the deposits in the Arisaig region as 

 the Listmore formation. 



So far as evidence goes in the Arisaig-Antigonish district, the 

 Listmore formation overlies the Ardness conformably. In def- 

 erence, however, to the determination of Fletcher, based on 

 observations made over a wide area, the age of these strata is 

 provisionally considered as Pennsylvanian, and a disconformity 



