THE DEVONIAN PERIOD 



131 



In the southern British Isles there are thick marine strata con- 

 taining much contemporaneous igneous rock (lava sheets), while in 

 the northern portion occurs the famous "Old Red Sandstone" 

 which is largely of continental origin. This sandstone attains a 

 greatest thickness of fully 20,000 feet, of which 6000 feet are inter- 

 bedded lavas and tuffs. Deposition of the sandstone appears to 

 have taken place, probably partly as delta and partly as wind-blown 



lb 



•? V j*\ Vtrltt III 







% jff\ ^^* : ^-j!^iilif r Nil 



itiWlllIIl V 





H l " ~ lllll 111 ! 



P^r 





■' : '^^-^m^^ 



>r-^ 









Fig. 72 

 Sketch map showing the general relations of land and water in Europe during 

 the Devonian. Horizontal lines = Early Devonian; vertical lines = 

 additional areas of Middle Devonian. (After De Lapparent, from 

 Chamberlin and Salisbury's "Geology," courtesy of Henry Holt and 

 Company.) 



deposits, in basins or lagoons more or less cut off from the open sea, 

 or at times in fresh-water lakes. Fossils are not abundant, but 

 they constitute a remarkable assemblage of land, fresh water, and 

 marine species scattered through various horizons. In many 



