Mc Learn —Silurian Arisauj Series of Arisaig, N. S. 1 29 



which twenty-three are confined to this formation. 

 Among the guide fossils are : Retiolites geinitzianus nmt. 

 venosus (Hall), Monograptus clintonensis (Hall), Cama- 

 rotcechia Uandoveriana var. rossbrookensis, n. var., 

 C. (Pectorhyncha) humiliplicata, n. sp., Plagiorhyncha 

 decemplicata (Sowerby), P. glassii (Davidson), P. plas- 

 tica, n. sp., Cwlospira hemispherica (Sowerby) and 

 Dalmanites weaveri (Salter). Chonetes tenuistriatus 

 Hall appears here for the first time. 



McAdavn formation. — The McAdam is made up of 1120 

 feet of gray and black shales and sandstones with a little 

 argillaceous limestone. Near the base is a three-foot 

 bed of iron-ore. The fauna totals forty-seven species, 

 of which twenty are restricted. The bivalves, for which 

 this locality is so noteworthy, now appear in abundance 

 for the first time and make up sixteen species of the 

 fauna. The guide fossils are: Dalmanella abdidimus- 

 cula, n. sp., D. elegantula var. transversomedia, n. 

 var., Camarot<vchia (Pectorhyncha) obtusiplicata (Hall), 

 Delthyris crispa (Hisinger), Honey mania planimargi- 

 nata, n. sp., and its variety elongimarginata, n. var.,. 

 Arisaigia postornata, n. sp., Orthonota arisaigensis, n. 

 sp., 0. pressiornata, n. sp., and Modiolopsis postunisul- 

 cata, n. sp. Chonetes tenuistriatus Hall makes its last 

 appearance here. 



Moydart formation. — This formation has a total thick- 

 ness of 380 feet. Impure limestone now becomes common 

 and the lithology consists of thin-bedded, flaggy and 

 ripple-marked greenish shales and arenaceous and argil- 

 laceous limestones. The fauna numbers thirty-four 

 species of which nine are restricted. The principal 

 guide fossils are : Eatonioides lamellornatus, n. sp., Wil- 

 sonia wilsoni var. saffordi (Hall), Delthyris crispa nmt. 

 moydartensis, n. nmt., Seelya moydartensis, n. sp. The 

 following are among those forms that appear here for 

 the first time and continue into the Stonehouse : Orbicu- 

 Joidea novascotica Ami, Chonetes novascoticus Hall, 

 Goniostropha aciculata (Hall), Calymene intermedia var. 

 antigonishensis, n. var., and Dalmanitina logani var. 

 conservatrix, n. var. 



The top 32 feet consist of massive red shale, without 

 fossils, and are thought to indicate a subaerial stage of 

 unknown duration. 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 266.— February. 1918. 

 9 



