260 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Ft. in. 



1 to 3. Yellowisli-vhite granular limeBtone, in beds of from 3 to 18 inches thick; often sepa- 

 rated by thin partings of green argillo-calcareous shale, which is also disseminated in 

 small patches through the bed 57 3 



4. Yellowieh-white granular limestone, in beds of from 6 to 18 inches thick; consisting of 

 masses of organic remains, of which crinoidal columns constitute the larger part; some 

 of them being three-fourths of an inch in diameter 16 



69 3 



This is the highest series of strata met with on the island, and its lithological characters 

 are so well marked that it is scarcely possible to mistake it for any of those which precede. 



For the sequence of faunal zones, according to which these lithologically similar 

 beds of argillaceous limestone and shale are distinguished by Logan, his original 

 account should be consulted. The general faunal relationships and correlation were 

 thus summed up by Billings : ^^^ 



MIDDLE SILUEIAN ANTICOSTI GROUP. 



Division 1 . — The rocks of division 1 rest directly and conformably upon those of the Lower 

 SUurianj above noticed, with no apparent physical gap between them, although there is a 

 paleontological break. It has been already stated that 41 of the species of the lower fauna 

 pass this break. They are here joined by 45 additional species, making the whole fauna of this 

 division to consist of 86 species, so far as is yet known. Of these, 18 pass upward into division 2, 

 13 into division 3, and 11 into division 4. 



Of the 41 species which are received from the Lower Silurian the following are known to 

 occur in Canada West and New York and are variously distributed throughout all the forma^ 

 tions from the base of the Quebec group to the top of the Hudson River formation. 



Stenopora fibrosa. 

 Halysites catenulatus. 

 Beatricea undulata. 

 Lingula quadrata. 

 Strophomena altemata. 

 S. planumbona. 

 Leptsena sericea. 

 Orthis porcata. 

 O. lynx. 



Orthisina verneulli. 

 Ambonychia radiata. 



Subulites elongata. 

 Mvtfchisonia gracilis. 

 M. ventricosa. 

 Bellerophon bUobatus. 

 Pterotheca transversa. 

 Orthoceraa formosum. 

 Ascoceras newberryi. 

 Asaphus megistos. 

 Calymene blumenbachi. 

 Cheirurus pleurexanthemus. 



Among the 45 species which here made their first appearance in the rocks of Anticosti we 

 find Strophomena rJiomboidalis, S. pecten, and Atrypa marginalis, all three very characteristic 

 of the Middle and Upper Silurian. The new species include Atrypa urnbonata and A. prinstana, 

 members of the group of which A. tumida may be regarded as the central form, a type ahnost 

 unknown in the Lower but very proHfic of species in the Middle and Upper Silurian. This* 

 group becomes extinct in the Devonian. The genera Favosites, HelioHtes, and Helopora, 

 which here first appear in force, are more characteristic of the upper than of the lower half of 

 the Silurian series. Most of the other new species belong to the ordinary Silurian genera. 



The fauna of this division is partly Lower and partly Middle Silurian but is more strongly 

 tinged with the former than the latter. 



Division 2. — From this division we have only 39 species, of which 18 are received from 

 division 1 and 21 here first made their appearance. Out of the whole fauna 23, or more than 

 one-half, pass into division 3 and 16 into division 4. As before stated, the only species very 

 characteristic of the Lower Silurian are Strophomena altemata and Murchisonia gracilis. The 

 most prominent fossil is Pentamerus harrandi, which occurs in vast numbers. Owing to the 

 inaccessible character of the coast in bad weather, it was not practicable to make a thorough 

 search for fossils in this division. 



