1 -is .}/<■/., iifii—Sihtriitii Arisaig Series of . 1 risaig, JV. S. 



Sciences at Yale University, and in particular to Pro- 

 fessors Joseph Barrel! and R. S. Lull. He is also 

 indebted in many ways to the officials of the Geological 

 Survey of Canada. More detailed acknowledgment will 

 be made in the final publication. 



Location. — The Silurian rocks of Arisaig occupy a 

 small area in northern Antigonish County, Nova Scotia, 

 on the shore of Northumberland Strait. The best sec- 

 tions are in the sea cliffs along the shore, and an almost 

 continuous exposure of the whole Arisaig series extends 

 from the small fishing village of Arisaig westward to 

 the vicinity of McAra's Brook. 



Stratigraphy. 



Arisaig series. — The name of Arisaig series has been 

 given by M. Y. Williams to the entire marine Silurian 

 column as developed at Arisaig. It has a total thickness 

 of about 3800 feet. The sediments are prevailingly argil- 

 laceous and consist of shales, sandstones and impure 

 limestone bands. Limestone, properly speaking, is 

 entirely absent. It has been divided by the cumulative 

 efforts of previous workers into five formations. In 

 ascending order, these are Beechhill, Ross Brook, 

 McAdam, Moydart and Stonehouse. Locally it is under- 

 lain by a flow of aporhyolite of Ordovician age, but Wil- 

 liams (1914) and others have shown that the relation to 

 the sediments of the Ordovician is that of an angular 

 unconformity. The Arisaig series is followed by the 

 subaerial strata of the Knoydart formation. 



Beechhill formation. — The Beechhill, the basal member 

 of the Arisaig series, has a thickness of about 200 feet 

 and is made up of sandstone and arenaceous shale with 

 a few local lenses of arenaceous limestone. The fauna is 

 a poorly developed one and only fourteen species are 

 recognized. The guide fossils are : Heliophrentis bilat- 

 eralis var. beechhillensis, n. var., Rhipidomella ari- 

 saigensis, n. sp., Camarotcechia bimesiornata, n. sp., 

 Whitfieldellaf crassa var. beechhillensis, n. var., and 

 Cyclonema parvimedium, n. sp. 



Ross Brook formation. — The Ross Brook consists of 

 about 830 feet of black, gray and greenish gray shales 

 and gray, somewhat lenticular, finely cross-bedded sand- 

 stones. The fauna consists of forty-three species of 



