Williams — Geology of Arisaig-Antigonish District. 245 



Devonian (Lower). 



1. Knoydart formation (Upper Devonian of Fletch- 

 er). — Hard, fine-grained, red, sandy slate, and 

 hard, gray sandstone, cut by small diabase 

 dikes. Thickness (outcrops measured by 



Fletcher; probably should be doubled), 683 feet. 



Silurian. 



Arisaig series (Silurian of Fletcher). 



1. IStoitehonse formation (= more or less of Lud- 



low of England). — Red shale and limestones, 

 argillaceous limestone and gray shales. Thick- 

 ness (Twenhofel), 1075 " 



2. Moydart formation (approximates the Louis- 



ville of United States, or Wenlock of Eng- 

 land). — The red stratum or red shale, argilla- 

 ceous limestone and shale. Thickness (Twen- 

 hofel), 379 " 



3. McAdam formation (Rochester of United 



States or upper Llandovery of England). — 

 Black shales and argillaceous limestone. 

 Thickness (Twenhofel) -I- iron-zone probably 

 100 ± feet, 1120 " 



4. Ross Brook formation (= Clinton of the United 



States, or lower Llandovery of England). — 

 Green shale with thin sandstones, dark papery 

 slates, etc. Obscure basaltic? intrusive. 

 Thickness (Twenhofel), 833 + " 



5. Beechhill Cove formation (= lower Clinton). — 



Sandstones, limestones and shales, resting on 

 aporhyolite flow and volcanic breccia. Thick- 

 ness (estimated from width of outcrop), 2(>0 " 



? Ordovician. 



1. Malignant Cove formation. — Coarse, cross bed- 

 ded, silicified conglomerates and grits ; irreg- 

 ular dikes of basalt. Thickness observed 

 (original thickness probably much greater),.. 20 ± " 



Upper Cambrian (Ozarkic). 



Brown's Mountain group (included in Cambro-Silu- 

 rian of Fletcher). 



1. Baxter's Brook formation. — Red and gray 



sandstones and schists, red and green slates ; 

 intruded by rhyolite necks and dikes, quartz 

 porphyry neck, diabase and basalt intrusives. 

 Thickness represented estimated at 500 " 



2. James River formation. — Flinty graywacke 



and grits, silicified banded slates; intruded by 

 i>ranite, rhyolite, diabase, basalt, and monzonite. 

 Thickness represented probably 1 mile ± 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 201.— September, 1912. 



17 



