154 W. H. Twenhofel — Silurian Section at Arisaig. 



19. Dark soft mud-shale with many fossils. Strike JS". 72° 

 W. ; dip 10° W. 



Thickness 24 feet. 



Dalmanella elegantula, Camarotmchia neglecta, Tentaculites, 

 Bucanella trilobata. 



20. Greenish -gray to dark arenaceous shale with more or 

 less thick beds of argillaceous limestones that are much veined 

 by quartz and calcite. Zone ends at mouth of McAdam brook. 

 Strike K 75°-80° W.; dip 40°- 48° W. 



Thickness __•. 123 feet. 



Fossils scarce except in a few lenticular limestones : Pholidops 

 imj)licata, Dalmanella elegantula, Camarotmchia neglecta, 

 C. cf. obtusiplicata, Tentaculites, Bucanella trilobata. 



21. Black, somewhat papery, soft carbonaceous shales with 

 no hard bands. Strike N. 64° W. ; dip 36° W. 



Thickness 30 feet. 



22. Dark-gray to black carbonaceous splintery shale with a 

 few hard bands and many oblate spheroidal concretions. 

 Strike JS". 65-80° W. ; dip 35-40° W. 



Thickness 144 feet. 



Dalmanella elegantula, Chonetes tenuistriatus, Camarotoe- 

 chia neglecta, C. obtusiplicata, Leptwna rhomhoidalis, Spiri- 

 fer crispus (first appearance), Grammy sia (small form), Caly- 

 mene tubercidata. 



23. Dark-gray to black soft carbonaceous shale. Strike 

 1ST. 70° W.; dip 39° W. 



Thickness 17 feet. 



Fossils as in 22. 



24. Dark-gray to black splintery arenaceous and finely 

 laminated carbonaceous shales. At various levels occur thin 

 beds of lenticular fine-grained sandstones and very large oblate 

 spheroidal concretions. Near the top is a bed thickly crowded 

 with pelecypods. Strike variable but in general N. 70° W. ; 

 with dip 45° W. 



Thickness 170 feet. 



Dalmanella elegantula, Chonetes tenuistriatus, Camarotoe- 

 chia neglecta, C. obtusiplicata, Atrypa reticularis, Spirifer 

 crispus, Grammy sia (small forms), Bucanella trilobata. 

 About thirty-five feet from the top occur Monograptus cf, 

 riccartoensis in great abundance. 



25. Dark-gray to black carbonaceous slaty shales in thick 

 beds with some lenticular fine-grained sandstones showing wavy 

 lines of lamination. Strike K 43°-54° W. ; dip 62° W. 



Thickness 44 feet. 



