136 ROYAL SOCIETY OF CANADA 



with the Upper Silurian as seen at Arisaig, a general resemblance will 

 be found from the volcanics of Frenchman's Barn to the base of the 

 red Lower Devonian sandstones of McAra's Brook. 



One peculiarity which we note about the Silurian cycle is the low 

 position in the series of strata occupied by the darlc shales. This may 

 be contrasted with the Laurentian cycle in which the black shale mem- 

 ber in the middle, (though there is also an uppei- black shale), the Lower 

 Huronian of Nova Scotia where it is at the summit, and the Cambro- 

 Ordovician where it is nearly as higli. In the Silurian in most sections 

 it is only a quarter, or, at most, a third from the base. 



The great regularity of this terrane in its gradual sinking and re- 

 elevation is seen in the different successive phases which follow each 

 other, not only in depth but laterally. The earliest phase or landward 

 cne shows no intercalated l)cds of marine origin which might have serve! 

 by their fossil shells to show the age of the plant beds, whose contents 

 are so unlike those of a similar age elsewhere. 



The best known section of this terrane is that of Arisaig, N.S., 

 where, according to Mr. H. Fletx-her, it has the following succession and 

 thickness ^ (the section is condensed) : — 



Medina — Gray flinty sandstone 200 



L. Clinton — Dark gray papery argillites 350 



TJ. Clinton — Green shales with flaggy layers 150 



Niagara — Greenish and dark shales and argillites 1,300 



L. Helderherg — Green and gray shales and flags. Eed marl at 



bottom 30 feet; red flags at top 100 feet 1,000 



3,000 



Lower Devonian Sub-cycle. 



Unlike the cycles of sedimentation previously described, this is but 

 a partial one. In New Brunswick it has only a littoral phase, as though 

 it were an incipient cycle of deposition suddenly cut oft' by the rising 

 of the sea bottom. It has been recognized only in several strips of 

 strata and one narrow basin at the Mispoc river. The fonnation is of 

 agglomerates, red conglomerates and red shales, which seem to have 

 been deposited imdcr perturbed conditions, as they contain no well pre- 

 served fossils, though they do have a few obscure plant remains. A 

 rolled boulder of Halysites caienidarins in the conglomerates at one 

 point, show it to be unconformable to and younger than the terrane last 

 described. 



^Rep. Prog. Can. Geol. Surv., 1886, p. 37. 



