FACTS AND OBSERVATIONS. 



xxi 



ceras nor any other Cephalopod appeared until near the end of this Stage D ; while in America 

 this order abounded in the Upper Primordial, and consisted of genera of every variety of rank 

 Piloceras, Lituites, Orthoceras, and Nautilus, the last genus being still an inhabitant of our seas. 



Gasteropoda are exceedingly numerous in America during this stage, and as remarkably few 

 in Europe. 



The Trilobites are nearly equal in number of species east and west of the Atlantic ; but the 

 geographical summaries exhibit many striking differences. The American Primordial has no dEglina, 

 Ogygia, &c., but has three Remopleurida , so abundant in Ireland and thus helping to connect 

 the western part of Ireland with the Silurian lands beyond the sea. It is to be remembered 

 that the great abundance of life in the Primordial of America need have no connexion with 

 priority, of existence, but may have arisen from a longer duration, from a more fertile epochal 

 impress, and from the much more extensive area of the western Primordial. During part of the 

 time the two great geographic divisions of this stage were coexistent. 



The Table (N) subjoined conveys only a provisional statement of the Primordial life of 

 America, but it is believed to be sufficiently accurate for general use. 



TABLE N. The Flora and Fauna of the Primordial Stage of North-east America ; principally the 

 River Ottawa, Lower Canada, the Mingan Isles, Western Newfoundland, and North-east 

 New York (not the Mississippi Valley). 



This stage is here divided into Lower and Upper Primordial, the former being represented by 

 Potsdam sandstone, and the latter by the enigmatical Quebec group and Calciferous sandstone, and 

 having superadded a few bottom layers of the Chazy beds of Lake Champlain. 



This separation is based on mineral, as well as on very striking organic characters. The 

 Table shows the latter at a glance. We there find seven important orders altogether absent from 

 the Potsdam sandstone, five very poor in species, while the Crustacea and Brachiopoda are 

 numerous. 



Speaking in general of the valleys of the St. Lawrence and the Mississippi, the Calciferous 

 sandstone overlies Potsdam sandstone conformably, but differs from it, chiefly, by containing more 

 lime or magnesia, and often more of both at once. The characteristic fossils of these beds, in the 

 districts here referred to, are not at all those of Potsdam rock, but are Gasteropoda and Cephalo- 

 poda in considerable numbers, and full of life and movement. It is poor in the other and simpler 

 orders. Of six it is altogether destitute. 



If we pass north-eastwards, from Quebec to the Mingan Isles in the Gulf of St. Lawrence, we 

 there find in this bed sixty-three fossils not often connected with those of the Quebec group. To 

 the south, in the Mohawk Valley, or to the west, in the valley of the Mississippi, we find the 

 same that is, numerous organic remains typical of place as well as of bed, 375 altogether. 



The Calciferous sandstone agrees with its associate strata in having neither Echinodermata nor 

 Monomyaria. 



The fossils of the subdivision Chazy, met with in the Quebec group, or its equivalent, about 



