282 



PALEOZOIC TIME. 





2. FOREIGN DEVONIAN. 

 I. Rocks: kinds and subdivisions. 



The Devonian rocks occur as surface-strata in most of the countries 

 of Europe, and. in parts of all the other continents. 



In the British Isles, they are exposed to view in southern Wales 

 and the adjoining county of Herefordshire ; in the peninsula of 

 Devonshire and Cornwall ; along the southern flank of the Grampians, 

 and on the northwestern side of Lammermuir from Dunbar to the 

 coast of Ayrshire, in the valley of the Tweed and elsewhere, in Scot- 

 land ; also in Ireland, and in the Isle of Man. 



On the map, Fig. 681 A, p. 344, the Devonian areas are distinguished 

 by vertical lines. 



The strata in England and Scotland have long gone by the name of 

 the Old Red Sandstone, — red sandstone being the prevailing rock in 

 Wales and Herefordshire, as well as in Scotland. In Devonshire and 

 Cornwall, these rocks are slates and limestone, instead of red sand- 

 stone. 



The beds of "Wales are argillaceous shales or marlytes, of red and other colors, with 

 some whitish sandstone and impure limestone, overlaid by red sandstone which passes 

 above into a conglomerate; and the whole thickness is estimated by Murchison at 

 8,000 or 10,000 feet. The limestone is concretionary, and is called Cornstone. 

 In Scotland, the following subdivisions have been made out : — 



( 3. Yellow sandstone ; containing Iloloptychius, etc. 

 3. Upper. ^ 2. Concretionary limestone. 



Red sandstone and conglomerate. 



2. Middle. 



.1 



11. 



( Gray sandstones and shales ; containing Onchus, Ctenodus, Polypterus, 

 ( Osteolepis, Pterichthys, etc. ^ 



3. Red and variegated sandstone. 



2. Bituminous schists; containing Dipterus, Pterichthys, Coccosteus, 

 Cephalaspis ; also Eurypterus, Pteryyotus, etc. 

 1 1. Conglomerate and red sandstone. 



In Devonshire and Cornwall, the strata are, according to Sedgwick: — 

 ( 2. Petherwin slate and Clymenia limestone. 

 ( 1. Marwood sandstones. 



( Roofing-slates and quartz, with variegated sandstones 

 I above, in north Devon. 

 3. Red sandstone and flagstone. 

 2. Calcareous slates. 

 1. Plymouth limestone. 

 1. Liskeard or Ashburton group. 

 The Clymenia limestone has been referred by some to the Lower Carboniferous. 

 In the south of Ireland, Devonian beds occur as a thin deposit in the counties of 

 Kilkenny and Wexford, rapidly thicken in Waterford, and have great bulk in Cork 

 and Kerry (Jukes). The rocks are red sandstones and slates, like those in the upper 

 part of the series in Wales. 



In the Eifel (Rhenish provinces), there are, below, slates and sandstones; next, the 

 great Eifel limestone, the equivalent, apparently, of the Corniferous; above this, slates, 

 with an intermediate limestone, — the whole termed the Cypridina slates, and perhaps 

 T ower Carboniferous in age. 



1. Lower 



4. Petherwin group. 

 3. Dartmouth group. 



2. Plymouth group. 



