PALEOZOIC TIME — UPPER SILURIAN. 563 



For a list of 163 Upper Silurian species found at Arisaig, Nova Scotia, see H. M. Ami, 

 I^ova Scotia List. Sc, 1892. In this paper Ami remarks on the relations of the fossils 

 that "they are much closer to the Ludlow rocks of Kendal, in Westmoreland, England, 

 than to either the Upper Silurian species of Anticosti, of Ontario, or those of the state of 

 New York." The species range from the Medina to the Lower Helderberg. 



Hall remarks that many Niagara species have their nearly related or representative 

 species in the Lower Helderberg : thus, Orthis elegantula is represented by 0. suhcarinata 

 and 0. perelegans ; 0. hybrida by 0. o&Zato and 0. discus; 0. puncto striata by 0. tuhxi- 

 lostriata; Spirifer Niagarensis by S. macropleurus ; S. sulcatus hj S. perlamellosus ; 

 S. C7'isptts by ^S*. cyclopterus; Stropho7nena (Orthothetes) subplana by S. (0.) Wool- 

 worthana. So also Fentamerus fornicatus of the Clinton is represented by P. galeatus. 



FOREIGN. 



The rocks of the Upper Silurian are widely distributed over the globe, 

 though less universal than those of the Lower Silurian. They occur in Great 

 Britain, Scandinavia, Russia, Germany, Bohemia, and Sardinia, and in Asia, 

 Africa, and Australia. They seem on a geological map to cover but small 

 areas, but only because they are concealed by later formations. 



The rocks in Great Britain where best displayed are subdivided as 

 follows : — 



1. May Hill (Gloucestershire) Sandstone, or Upper Llandovery group. — 



Sandstones, with some arenaceous limestone ("Pentamerus limestone"), 

 which terminate above in the Tarannon shales. — American Equivalent, the 

 Medina and Clinton groups. 



2. Wenlock Group. — Consists of (1) the Woolhope beds, limestone and 

 shale; (2) Wenlock shale; (3) Wenlock or Dudley limestone. — Amer. 

 Equiv., the Niagara shale and limestone. 



3. Ludlow Group. — Consists of (1) the Lower Ludlow rock; (2) the 

 Aymestry limestone ; (3) the Upper Ludlow ; (4) Tilestones. — Amer. Equiv., 

 the Onondaga and Lower Helderberg groups. 



These subdivisions are well exhibited in Shropshire or western England and 

 in eastern and southern Wales. Between the Tilestones and the Ludlow are 

 one or two thin bone-beds consisting of remains of Fishes and Crustaceans. 

 In ls"orth A¥ales, and in AVestmoreland, Cumberland, southern Scotland, and 

 southwestern Ireland, the beds are mostly grits and shales, and are m.uch 

 upturned, with the subdivisions not distinct. The Wenlock group is repre- 

 sented by the Denbighshire grit in North Wales, and the Coniston grits in 

 Cumberland. The thickness is stated to be from 3000 to 5000 feet. 



Upper Silurian beds outcrop : in Russia over a large area south of the Gulf 

 of Finland ; in southern Sweden ; about Christiania and some points to the 

 north in Norway ; in the Bohemian basin near Prague, where Barrande's 

 formation E corresponds to the Niagara and Onondaga periods, and his 

 E, G, H, approximately to the Lower Helderberg and Oriskany ; in the 

 Fichtelgebirge ; and the upper section only in the eastern Hartz, where the 



