308 



of the habitat, which was extremely unfavourable to the 

 corals, crinoids, bryozoa and many brachiopods, but appar- 

 ently favourable to the pelecypods and not harmful 

 to the trilobites. 



The Silurian fossils of Arisaig in aspect are more Euro- 

 pean than American, but yet are unlike those of either 

 country. Other than such cosmopolitan species as Dal- 

 manella elegantula, Leptaena rhomboidalis, Camaro^oechia 

 neglecta, Anoplotheca hemispherica, and Atrypa reticularis, 

 there is little else in the faunas that occurs elsewhere. 



By reason of its nearness, the Anticosti faunas apparently 

 should show close relations with those of Arisaig and 

 although separated by less than 250 miles (400 km.), 

 the two regions have less than ten species in common. 

 The only portion of the Anticosti series with which a 

 stratigraphic correlation can be definitely made is the 

 lower Jupiter River formation in which are found Mono- 

 graptus dintonensis , Dalmanella elegantula, Plectamhoniies 

 transversalis, Leptaena rhomboidalis, Anoplotheca hemis- 

 pherica, and Calymene tuber culata, all of which species 

 are also present in the upper 633 feet (193 m.) of the Ross 

 Brook formation. The Jupiter River sediments which 

 contain these species are 80 feet (24 m.) thick and consist 

 of highly calcareous shales which are succeeded by deposits 

 containing a greater lime content and preceded by a 100 

 foot zone of slightly sandy shale underlain by sediments 

 rich in lime. At Arisaig Atrypa reticularis appears for 

 the first time in the second zone of the McAdam formation, 

 but on Anticosti it makes its appearance below the 

 Monograptus dintonensis horizon. Its later appearance 

 at Arisaig may be due to the great amount of mud in 

 the Ross Brook sea. The 80 feet of the Jupiter River 

 rocks are the time equivalents of at least a part and 

 perhaps the whole of the 633 feet of the Ross Brook for- 

 mation, since it is very probable that the latter were 

 accumulated far more rapidly than the former. 



The succeeding Jupiter River rocks would correlate 

 with the lower McAdam formation, but there is no simi- 

 larity in either the lithology or the faunas. The Chicotte, 

 the closing formation of the Anticosti series, carries a 

 pronounced coral fauna and its rock consists largely of 

 coral-reef limestone. Nothing similar exists in the Mc- 

 Adam formation, from which not a single coral has ever 

 been collected. It is believed that the striking faunal 



