1 30 McLearn— Silurian Arimig Series of Arisaig, N. S. 



Stonehouse formation. — This, the terminal member of 

 the Arisaig series, has a thickness of 1275 feet and con- 

 sists of gray, green and red thin-bedded, ripple-marked 

 shales, sandstones and impure limestones. Two hundred 

 feet of strata on Stonehouse Brook are now recognized 

 for the first time and added to the top of the section. 

 The fauna numbers ninety-four species, of which fifty-six 

 are restricted. The principal guide fossils are : Lingula 

 minima (Sowerby), Dalmanella lunata (Sowerby), Bla- 

 cky prion gilpini (Dawson), Camarotocchia glomerosa, n. 

 sp., Delthyris rugicosta (Hall), D. rugicosta var. subsul- 

 cata (Hall), Grammy sia triangulata (Salter), G. obliqua 

 ( McCoy), Palceoneilo attenuata (Hall), Nuculites concen- 

 tricus var. subequilatus, n. var., Arisaigia placida Bil- 

 lings, A. placida var. socialis (Billings), Tropinuculites 

 carinatus (Hall), Pterinea honey mani (Hall), Palceopec- 

 ten danbyi (McCoy), Goniophora (Cosmogoniophora) 

 bellula (Billings), Modiolopsis exilis Billings, M. rhom- 

 boidea (Hall), Orthonota angulifera (McCoy), 0. incerta 

 Billings, Orthoceras antigonischene, n. sp., Dawsono- 

 ceras elegantulum (Dawson), Homalonotus daivsoni 

 Hall, Dalmanitina logani (Hall), and Leper ditia sinuata 

 Hall. Other common forms, but not restricted to this 

 formation, are: Chonetes novascoticus Hall, Calymene 

 intermedia var. antigonishensis, n. var., Nuculites con- 

 centricus (Hall), N. concentricus var. subovatus (Hall), 

 N. cawdori (Sowerby), N. cawdori var. elongatus (Hall), 

 N. cawdori var. erectus (Hall) and Kionoceras angula- 

 tum (Wahlenberg). 



Physical conditions. 

 Two dominant bottom conditions are recorded by the 

 lithology. One is a mud habitat, the life of which is now 

 enclosed in shale. The other is a shelly bottom, mixed 

 with mud or sand and now recorded by the impure shelly 

 limestone layers. The absence of pure limestone shows 

 that clear waters never existed for any length of time. 

 The series was probably laid down in a shallow marginal, 

 but normally marine, sea, into which flowed silt-laden 

 rivers from an elevated landmass. 



Biological associations. 

 The faunal associations are somewhat unusual and 

 merit consideration. One notes the absence of many 



