446 



CANADIAN EQUIVALENTS. 



[Ch. XXVII 



erroneously identified, an error to which he confesses that he himself con- 

 tributed ; and on the whole these lower beds contain, he thinks, a very 

 distinct set of species, only three or four of them out of eighty-three 

 passing upwards into the incumbent formations/'^ 



Be this as it may, the Black River Limestone, No. 15, contains certain 

 forms of Ortlioceras of enormous size (some of them 8 or 9 feet long !), 

 of the subgenera Ormoceras and JEndoceras^ seeming to represent the 

 Lower Silurian or Orthoceras limestone of Sweden. Moreover, the gen- 

 eral facies of the fauna of all these beds is essentially similar. Another 

 ground for extending our comparison of the Llandeilo beds of Europe as 

 far down as the calciferous sandstone is derived from the researches of 

 Mr. Logan in Canada, and the study by Mr. Salter of the fossils collected 

 by the Canadian Surveyor near the S. E. end of the Ottawa River, where 

 one mass of limestone incloses species common to all the beds from the 

 Calciferous Sandstone (No. 18) up to the Trenton Limestone (No. 14). 

 In this rock, the Asa^^hus gigcts and other well-known Trenton species are 

 blended wdth the Maclurea (a left-handed Euomphalus^ fig. 606), a genus 



Fossils, f r oin Allumette Hapids, River Ottawa^ Canada. 

 a Tig. 606. 



Maclurea Logani, Salter. 

 a. View of the shell. h. Its curious operculnm. 



characteristic of the Chazy Limestone, or No. iV ; 

 and Miirchlsonia gracilis (fig. 607) is another 

 Trenton Limestone species found in the same Silu- 

 rian limestone of Canada ;f while one of the most 

 common shells in it is the Raphistomo, ? i^Euom- 

 phaliis) uniangulatum^ Hall, a species character- 

 istic in New York of the Calciferous Sandstone 

 itself. 



In Canada, as in the State of New York, the 

 Potsdam Sandstone underlies the above-mentioned 

 calcareous rocks, but contains a different suite of 



fossils, as will be hereafter explained. In parts of the globe still more 

 remote from Europe the Silurian strata have also been recognized, as in 

 South America, Austi'aha, and recently by Captain Strachey in India. 

 In all these regions the facies of the fauna, or the types of organic life, 

 enable us to recognize the contemporaneous origin of the rocks ; but the 

 fossil species are distinct, showing that the old notion of a universal dif- 

 fusion throughout the " primaeval seas" of one uniform specific fauna was 



* Hal] ; Forster and Whitney's Report on Lake Superior, Pt. II. 1851. 

 f Logan, Report Brit. Assoc. Ipswich, pp. 59, 63. 



IfurcMsonia gracilis, Hall. 



A fossil characteristic of the 

 Trenton Limestone. The 

 genus is common in Lower 

 Silurian rocks. 



