14 G. P. MATTHEW ON THE 



dam Group " (Lower Cambrian) is aboiit 2,000 feet thick. Another portion which he calls 

 Potsdam and Calciferons (D-H) is about 1,800 feet thick ; as its lower member [D) contains 

 Lino'ula acuminata the whole may be Upper Cambrian. Above this comes a remarkable group 

 of beds (I-N), whose fauna Mr. Billings compared to that of the Chazy and Calciferons, 

 hut which Sir Wm. Logan called " Upper Calciferons." All these are below the shales 

 which carry the Levis or Arenig graptolites, and so must be regarded as apart of the 

 Cambrian, by those who consider these graptolites as marking the base of the Ordovician 

 system. 



A remarkable feature of the upper part of the Cambrian at the Strait of Belle Isle is, 

 that many of the moUusca are similar to those of the Black River limestone.' Mr. Billings 

 found that the upper member (TV) carried a fauna very like that of the Orthoceratite lime- 

 stone of Sweden and the Pleta limestone of Russia, both of which are above the beds 

 which in those coirntries hold the Arenig graptolites. If these graptolites be accepted as 

 cotemporaneous on the two sides of the Atlantic the moUuscan fauna, in the one case 

 above them and in the other below, must be older in America than in Europe. 



The disturbed region occupied by the well-known Levis shale and other rocks of Sir 

 Wm. Logan's Quebec Group, divides this eastern outlier of the Calciferous-Chazy fauna 

 from the typical regiou where this fauna was originally studied. In the latter region 

 occur several peculiar gasteropods, Ophileia compacta, Maclurea magna and M. Logani which 

 are good examples of a variety of similar forms which swarmed in the seas of that 

 period. 



The Chazy rocks which contain these fossils have been traced along the course of the 

 great lakes, through Manitoba, by King William's and Grinnell Land to the Arctic Sea. 

 The same fairna is found in Scotland and Sweden ; here, however, it succeeded the Arenig 

 fauna of graptolites. In the south of Scotland this shallow-water fauna was extinguished 

 by the submergence which brought in the Llaudeilo graptolites. Lituites of the Calcifer- 

 ons terrane and a group of Cephalopods characteristic of the Chazy in America appears on 

 the other side of the Atlantic in the Llaudeilo beds of Great Britain and the Orthoceratite 

 limestone of Sweden. Other genera might be cited to show the .slov^' translation of the 

 shallow-water species of this period from America to Europe. 



Among the brachiopods one may take the well-known Strophomena as an instance 

 of a migrating genus. A small species of this genus occurs in Band a of Division 3 

 (Bretonian) of the St. John Group near the horizon oî Parabolina spinu/osa. This species 

 was displaced in Acadia by the invading Dictyouema fauna and driven to some other part 

 of the Cambrian Sea. Perhaps to the north, for at a somewhat later date there occurred 

 there a species, S. Aurora, Billings, similar to the Acadian species ; this species is spread 

 through a considerable thickness of the "Upper Calciferons " beds near the Strait of Belle 

 Isle, to which we have referred above. Of a still later date are the two species of this 

 genus which Dr. Brogger found in the Orthoceratite limestone of Norway. One of these 

 which he compares to S. imbrex, Pand., resembles Billings's species cited above. Stropho- 

 mena in its typical development, howcA-er, is an Ordovician genias, and even extends 

 irpWiird through the Silurian. 



A few species, according to Billings, are identical with species found in that limestone. 



