294 PALAEOZOIC TIME — DEVONIAN AGE. 



tions are among the most extensive in the geological series, and 

 crinoidal remains are in great profusion. 



FOREIGN DEVONIAN. 



I. Rocks : kinds and subdivisions. 



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

 tries 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 Gram- 

 pians, and on the northwestern side of Lammermuir from Dunbar 

 to the coast of Ayrshire, in the valley of the Tweed, and elsewhere, 

 in Scotland ; and also in Ireland and the Isle of Man. 



On the map, fig. 605, 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 Scotland. With the sandstone, 

 there are beds of marl or argillaceous shale, and some limestone. 



The beds of Wales are argillaceous shales or marls, 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 8000 or 10,000 feet. The limestone is concretionary, and is 

 called Corn-stone. 



In Scotland there are, according to Hugh Miller, the following subdivisions : — 



{3. Yellow sandstone ; containing Holoptychius, etc. 

 2. Concretionary limestone. 

 1. Red sandstone and conglomerate. 

 2. Middle — Gray sandstones and shales ; containing Cephalaspis, etc. 



C 3. Red and variegated sandstone. 

 , T j 2. Bituminous schists ; containing Dipterus, Pterichthys, Coccos- 



teus, etc. 

 ^ 1. Conglomerate and red sandstone. 

 In Devonshire and Cornwall the strata are of very different character. They 

 are stated by Sedgwick as follow : — 



4. Petherwin group. ( 2# Petherwin slate and Clymenia limestone. 



(. 1. Marwood sandstones. 

 3 Dartmouth eroun I Roofing-slates and quartz, with variegated sandstones 



( above, in north Devon. 



{3. Red sandstone and flagstone. 

 2. Calcareous slates. 

 1. Great Devon limestone. 

 1. Liskeard or Ashburton group. 



