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THE ARISAIG FAUNAS AND THEIR CORRELATES. 



Lower Ordovician. — Obolus {Linguloboliis) spissa from the 

 upper James River slates also occurs in or associated with 

 the oolitic iron ores of the Lower Ordovician of 

 Belle Isle, Conception bay, Newfoundland. The occur- 

 rence of the same species with similar deposits at Arisaig 

 leads to the correlation of the Arisaig measures with the 

 Belle Isle rocks. The close stratigraphical relations of 

 the Baxter's Brook beds with those of the James River 

 hardly permits their separation and they are included 

 therewith and considered part of the same system. 



Ordoviciani — The Malignant Cove formation contains 

 no fossils so that its age determination depends on super- 

 position. Since it is separated from the Lower Ordovician 

 rocks by both an erosional and structural unconformity and 

 appears to lie below the Silurian, it has been referred to 

 the Ordovician (Williams). 



Silurian. — The rocks of the Arisaig series are abundantly 

 fossiliferous, but careful and painstaking collecting is 

 required. Free fossils are not common. The number 

 of species was given by Ami in 1891 as 162, of which about 

 100 have been described; but it is safe to say that the 

 collections now in the various museums, particularly 

 those of the Canadian Geological Survey, the U. S. National 

 Museum, and Yale, will largely increase the above number. 



The Silurian faunas taken as a whole predominate in 

 pelecypods, as fully one- third of the species and specimens 

 belong to this class of invertebrates. Brachiopods, 

 generally the most abundant of Silurian fossils, at Arisaig 

 hold second place, which place is attained by reason 

 of the occasional deposition of lenses of relatively pure 

 limestone and not because they are abundant in the 

 sediments as a whole. Cephalopods and gastropods 

 are about equally represented, though neither group has 

 more than half a dozen species. Bryozoa and corals, 

 usually so abundant in strata of this age, are almost wholly 

 absent, the former being present in but a few stems of a 

 ramose Monticuliporoid, while of the latter only a few 

 specimens of a single species have been collected. Trilo- 

 bites are relatively abundant. These faunal peculiarities 

 with but little doubt are caused by the muddy character 

 35063— 7iA 



