296 



The deposits are probably not of marine origin, this con- 

 clusion being based on the absence of marine fossils and 

 the poorly bedded and little sorted character of the sed- 

 iments. 



Silurian. Arisaig Series. 



Where the base of the Silurian has been seen it rests on 

 the eroded surface of a rhyolite flow extruded before the 

 marine overlap of Arisaig time. The fault of the Hollow 

 separates the Silurian from the Ordovician. On lithologi- 

 cal grounds the strata can be placed in two subdivisions; 

 the lower portion consisting almost entirely of shales, has 

 a thickness exceeding 2000 feet (510 m.) while the upper 

 shales and impure limestones are 1454 feet (373 m.) thick. 

 The character of the sediments denotes proximity to the 

 shore, a conclusion confirmed by the pronounced develop- 

 ment of ripple marks, cross-lamination, and small lenses 

 of sandy and impure limestone. On the basis of lithology 

 and faunal differences the Arisaig series can be divided into 

 five well marked formations to which, beginning at the 

 base, the names of Beech Hill Cove, Ross Brook, McAdam, 

 Moydart, and Stonehouse have been applied. 



Beech Hill Cove formation. — This formation consists of 

 greenish calcareous sandstones, sandy impure limestones 

 and grey sandy shales. At the type section and at Doctor's 

 brook the strata have an almost vertical attitude. The 

 formation is poorly exposed at Arisaig point. Along the 

 line of the Intercolonial railroad on Barney's river, opposite 

 the mouth of Bear brook, and again at Marshy Hope, are 

 outcrops of strata which probably belong to this forma- 

 tion. Fossils are nowhere abundant but the following have 

 been recognized: Zaphrentis cf. hilateralis, Lingiila cf. 

 ohlonga; Dalmanella cf. elegantula, and Cornulites flex- 

 uosus. The thickness has never been accurately deter- 

 mined. The present writer estimated the Beech Hill Cove 

 outcrop at 160 feet (48 m.) while Williams gives the thick- 

 ness as 200 feet (61 m.). 



Ross Brook formation. — The strata of the Ross Brook 

 are divisible into two divisions, a lower one (zone i) of 

 black papery shales with a thickness of about 200 feet 

 (61 m.) from which no graptolites have been collected, and 

 an upper division, 633 feet (193 m.) thick, throughout 

 which graptolites are present in abundance. The upper 

 division is again readily divisible into a lower subdivision 



