PALEOZOIC TIME — UPPER SILUEIAN. 535 



The Ural Mountains include long ranges of upturned and more or less 

 crystalline Lower Silurian rocks, but it remains undetermined whether or not 

 there is unconformability with the Upper Silurian beds. 



Of the 204 species of fossils in 68 genera, found in the Lower Lland- 

 overy beds, 104 species in 45 genera still exist in the Upper Llandovery. 

 (Etheridge.) 



NEOPALEOZOIC SECTION. 



In contrast with the Eopaleozoic part of geological history, when vast 

 continental seas prevailed, — a condition well styled thalassic,^ both as 

 regards geography and life, — the Neopaleozoic was the time of the in- 

 creasing emergence of the land over large areas, and the emergence also of 

 life in various forms, until in eastern North America a great semi-continent 

 existed, over 1000 miles wide, which was covered with grand forests and 

 other vegetation, and populated by Amphibians and Reptiles of ancient 

 kinds, and by the largest of Insects, besides other inferior terrestrial 

 Invertebrates. 



UPPER SILURIAN ERA. 



Stnoxymt. — Upper Silurian, Murchison, Phil. 3Iag., vii., July, 1835; Bep. Brit. 

 Assoc, Aug., 1835; Silu7: System, 1838. Upper part of Silurian, Sedgwick, Rep. Brit. 

 Assoc, 1835; Proc G. Sac, 1838; Q. J. G. Soc, Jan., 1846. Silurian, Sedgwick, 

 Q. J. G. Soc, 147, 1852 (the Lower Silurian being made Upper Cambrian); Lapworth, 

 G. Mag., 1879, p. 13 ; H. B. Woodward, Geol. Eng. and Wales, 1887. Murcliisonian, D'Or- 

 bigny, Pal. et Geol.., ii., 301, 1851. Boliemien, A. de Lapparent, Tr. de Geol., 1883. 



NORTH AMERICAN. 



Subdivisions. 



( 3. Upper Pentamerus epoch. 

 3. Lower Helderberg ] ^^ g^^^^^ iin,estone epoch. 



( 1. Lower Pentamerus epoch. 

 2. Onondaga Period. — Salina beds, Water-lime, Tentaculite limestone. 



( 3. Niagara epoch. Shale and limestone. 

 1. Niagara Period. < 2. Clinton epoch. Clinton group. 



Vi 



Medina epoch. Oneida and Medina beds. 



The map on page 536 (Eig. 737) presents a general idea of the dry 

 land of North America at the opening of the Upper Silurian. The shore line 

 of the time was not far outside of the Archaean limits (indicated by the 

 dotted line), showing that the growth of the continent had been mainly 

 along its Archaean borders. There was an extension of the land over the 



1 With Homer, the QdXacra-a was the great Interior Continental Sea, the Mediterranean, while 

 the outside waters around the land were called '^Keavos. The term thalassic is used above in 

 the Homeric sense. 



