306 PALEOZOIC TIME. 



same infusorial origin as that of other formations (p. 257) ; and so 

 also the quartz constituting the geodes. Beyond this, the origin of the 

 geodes has not been explained. 



2. Foreign Subcarboniferous. 



The Subcarboniferous period was a time of limestone-making also 

 in Britain and Europe. There is proof, therefore, of a wide extension 

 of those geographical conditions that characterized America, — that 

 is, of an extensive submergence of the continental lands, as a prelude 

 to the period of emergence and terrestrial vegetation that followed. 

 Moreover, the later part of the series is most purely limestone, the 

 earlier in many places consisting of shale or sandstone. The lime- 

 stone is often called the " Mountain limestone." 



In Great Britain, the limestone occurs in portions of South and North Wales, and near 

 Bristol, 500 to 1,500 feet thick; in Derbyshire and North Straffordshire, in central Eng- 

 land, 1,000 to 4,000 feet; in Cumberland, in Northern England, 1,000 to 1,500 feet; 

 along the midland counties of Scotland, but of little thickness compared with that in 

 England ; in Ireland, with a thickness of 3,000 feet or more. 



There is more or less of shale or sandstone in the limestone formation of these 

 regions. In Wales, the limestone is underlaid by 200 to 300 feet of Subcarboniferous 

 shale, and in Ireland, by 500 to 5,000 feet of shale and sandstone. The series in 

 southern Ireland includes 2,000 feet of Subeai-boniferous shale, resting on 3,000 feet of 

 grit called the Coomhola grit, and that on reddish Devonian sandstones ; and that of 

 northern Ireland consists of (1) 500 feet of yellow sandstone, and (2) 2,700 feet of 

 limestone, with some intercalcated shale and sandstone. The Coomhola grit is referred 

 by some geologists to the Devonian; but it includes nearly the same fossil shells as 

 the slate above, along with abundance of Spirifer dkjunctus, Spirifer cuspidatus, and 

 other Subcarboniferous forms. 



In Belgium, near Liege, there are, at base, shales and sandstone overlaid by Crinoidal 

 limestone, partly cherty; together they constitute the Condrusian system of Dumont. 



Over Russia — a great Interior Continental region like that of North America — the 

 Subcarboniferous rocks are mainly limestone, and have a wide distribution. The for- 

 mation is well displayed, according to Murchison, on the western flank of the Ural 

 Mountains, upturned, and overlying the Devonian, and along parts of the Volga. 

 Near Moscow, it has been reached by boring through the Jurassic and Coal-measures. 



In the Subcarboniferous limestone of Great Britain, there are beds of trap and other 

 igneous rocks. In Durham and Northumberland, the interstratified sheets of basaltic 

 rock extend for miles. In Scotland, the interpolations of trap, porphyryte, and tufas 

 are numerous, and occur throughout the series, especially its lower part. They form 

 a conspicuous chain of terraced heights, from near Stirling, through the range of the 

 Campsie, Kilpatrick, and Renfrewshire hills, to the banks of the Irvine in Ayrshire, 

 and thence westward by the Cumbrae Islands and Bute to the south ofArran. 

 (Geikie. ) In Ireland, county of Limerick, there are masses of trap 1.200 to 1,300 feet 

 thick, with tufaceous beds, intercalated with the limestone strata. 



Life. 



Plants. — Small coal-beds and a number of species of coal-plants 

 occur in the strata. The plants are related to those of the lower part 

 of the Coal-measures, and are, for the most part, the same in species. 



