398 THE DEVONIAN PERIOD 



the Ordovician through the Carboniferous. Of 30,000 feet of 

 Palaeozoic rocks, 6000 feet of limestone and 2000 feet of shale 

 are assigned to the Devonian. Beyond the long, narrow strip of 

 land which lay along the western side of the Great Basin, the 

 Devonian reappears ill California. 



Foreign. — The European Devonian appears under two very 

 different fades, or aspects of development ; one of these is the 

 " Old Red Sandstone," which was laid down in closed basins 

 having restricted or occasional connection with the sea, and the 

 other is the ordinary marine type. The period began in Europe 

 with an advance of the sea over the land in many places, reaching 

 its maximum extension in the latter part of the period, but begin- 

 ning to retire before the opening of the Carboniferous. The 

 movement of depression was at first only sufficient to permit the 

 accumulations of shallow-water deposits, which in the Rhine dis- 

 trict attain the great thickness of 10,000 feet. The Middle Devo- 

 nian in the same region is prevailingly a great limestone, and the 

 Upper is made up of limestones and slates. This subsidence re- 

 moved the barrier which in Ordovician and Silurian times had 

 separated the northern and southern seas, but was accompanied 

 by the formation of closed basins farther to the north. Europe 

 then was largely an open sea with many islands, and where the 

 waters were sufficiently clear and free from terrigenous sediment, 

 coral reefs were extensively formed. 



The marine Devonian occurs in the southwest of England, 

 over large areas of Germany, in northwestern and southern 

 France, and on an enormous scale in Russia. During the Silu- 

 rian the sea had withdrawn almost entirely from Russia west of 

 the Ural Mountains. In the Lower Devonian the sea broke in 

 from the north over Siberia, reaching far into central Asia. In 

 the Middle Devonian a great basin was formed by the depression 

 of central Russia, the sea advancing from the north and the east. 



The " Old Red Sandstone" is of particular interest, because, 

 owing to the peculiar circumstances of its formation, it has pre- 

 served a record of Devonian land life, which, though fragmentary, 

 is far more complete than anything we possess from the more 



