212 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



M. 



Feet. 



1. Brownisli-gray limestone, in beds varying in thickness from 6 inches to 6 or 7 feet, inter- 



stratified at distant intervals with reddish-gray dolomite in beds of from 3, to 9 inches, 

 which constitute 1 or 2 per cent of the whole. Both the limestone and the dolomite are 

 fossiliferous throughout; the organic forms, however, are obscure in the whole, with the 

 exception of about a foot of the limestone at the base and 6 feet at the top, including a bed , 

 of the dolomite, in the whole of which the fossils are silicified. The genera at the base are 

 Eospongia, Orthis, Ophileta, Pleurotomaria, Murchisonia, Orthoceras, and Asaphus. At 

 the top the same genera occur, but there is a greater number of species, and it is probable 



that the fossils of these two parts represent those of the whole mass 350 



In the fossiliferous beds of divisions K and L, and in part 1 of M, there are several species 

 of each genus, and the same species seem to range through the whole. The described 

 species are Orthis electra, Maclurea matutina, and Orthoceras piscator; but the chief part of 

 the species of the remaining gastropods and cephalopods are so closely allied to some of 

 the common forms of the Trenton group that it scarcely appears doubtful that they are the 

 same. The most striking resemblances are to Orthoceras bigsbyi and 0. allumettense of the 

 Birdseye and Black Kiver, and to Murchisonia gracilis, M. bellidncta, and M. perangulata 

 of the Trenton formation. 



2. Bluish-gray limestone, in beds varying from 6 inches to 10 feet in thickness, the thicker 



beds being made up of layers of 1 or 2 inches, distinguishable in section by slight differ- 

 ences in color but without any tendency to separate. Some of the beds are nodular and 

 crumble under atmospheric influences. Fossils are abundant in all the beds but are not 

 readily separated. They consist chiefly of Stenopora fibrosa, Orthis like 0. platys, Rhyn- 

 chonella allied to R. plena, Camerella varians, new species of Maclurea, and Orthoceras; 

 with 0. piscator, 0. allumettense?, 0. bigsbyi?, Amphion, Ampyx, Asaphus, lUsenus, and 

 Leperditia .' 308 



1,349 



Commenting on the above section, Ulrich suggests upper Beekmantown for 

 division I and middle Chazy for division M. 



Billings ®^^ discusses in the following teitos the taxonomic relations of the Ordo- 

 vician strata of Newfoundland which constitute Logan's divisions I, K, L, and M.: 



These four divisions consist of 235 feet of magnesian limestones at the base, above which 

 we have 844 feet of light bluish-gray limestones, making in all a thickness of 1,084 feet. , Only 

 37 species of fossils hare been collected in this series of beds; and of these, nine species are 

 found in division H below, while ten of them pass upward into division N next above. Three 

 of the species {Stromatopora compacta, Orthoceras allumettense, and Asaphus canalis) occur in 

 Canada, the first two in the Chazy and Black River and the last in the Calciferous and Chazy. 

 The following are closely allied to Black River and Trenton species: 



Ctenodonta angela, allied to C. contracta, B. R. 

 Subulites daphne, allied to S. parvulus, B. R. 

 Murchisonia simulatrix, allied to M. gracilis, B. R. and Tr. 

 Murchisonia cicelia, allied to M. perangulata, B. R. 

 Murchisonia sororcula, allied to M. perangulata, B. R. 

 Murchisonia augustina, allied to M. bellicincta, Tr. 

 Orthoceras hsesitans, allied to 0. bigsbyi, B. R. 



The occurrence of great numbers of individuals of these species in a silicified condition 

 and weathered out in bold relief gives to the slabs of limestone an aspect so remarkably like 

 that, of the well-known specimens from Pauquettes Rapids that at first sight one might be 

 well led to say. This is surely the Black River limestone. But on careful comparison of perfect 

 specimens it is seen that notwithstanding the resemblance none of the species are strictly iden- 

 tical. All present such differences that after a study of collections from both localities they can 

 be separated if mixed up together without their labels. Even 0. allumettense, which I have 

 identified, differs by being much larger than any Specimens that have been seen in the original 

 localities. 



