CJHKAT BRITAIN 



371 



and various schists, with occasional crystalline 

 limestones the whole series being veined more or 

 lew* abundant l\ \\ith pegmatite. Small isolated 

 areas of Aivh:ean occur also in England (Charn- 

 \\ood Forest, the Wrekin, tin- Mahcrns). No 

 i..--iU are met with in any of the Arch;. -an 

 roeks. 



'I'll.- oldest fossiliferous strata in Britain belong 

 to the < 'amhrian System (q.v.), and are well de- 

 \cloped in Wales and Shropshire, attaining a thick- 

 in--, of morn than :{<),000 feet. They consist chi.-lly 

 of .lark red and purple sandstones, grits, and con- 

 glomerates, with green slates and slaty shales. 

 Tin- t'ossils are not abundant, but show a remark- 

 variety of forms. In Scotland the Cambrian 



appears to !>. represented by the red grits, con- 

 glomerates, and sandstones which rest directly on 

 the Arcli:i-an rocks of the outer Hebrides and the 

 north west Highlands. 



The S// ii rili ii Xyv/o/i (Q.V. ) occupies a large por- 

 tion of the surface of tne country. The typical 

 roeks occur in Wales, extending over the western 

 portion of the principality from Pembroke to 

 Denbigh, and including the northern portions of 

 IVmliroke. Carmarthen, and Brecknock, the whole 

 of Radnor and Montgomery, the south-west of 

 Denbigh, and the whole of the counties to the west. 

 The oldest or Lower Silurian beds are next the 

 coast. The series consists of an immense thickness 

 of shales, slates, grits, and greywackes, with inter - 

 calated limestones more or less pure. Immense 

 tracts have hitherto proved devoid of fossils; in 

 other districts the calcareous rocks are almost 

 entirely composed of the remains of marine in- 

 vertebrate animals, while the shales abound in 

 zoophytes and Crustacea. The high lands in the 

 north of Lancashire and south of Westmorland 

 are Silurian ; but it is in Scotland that these 

 strata are most extensively developed. A line 

 drawn from Dunbar to Girvan forms the northern 

 limit of these beds in the south of Scotland. Ex- 

 cept the lower half of the valley of the Tweed, the 

 whole region from this line to near the base of the 

 Cheviots is Silurian. The rocks are chiefly grey- 

 wacke, with scattered beds of impure limestone. 

 The chief fossils are graptolites, Crustacea, hrachio- 

 poda, and mollusca. The lead-mines of Wanlock- 

 nead and Leadhills are in this district. East and 

 smith-east of the Archaean and Cambrian rocks of 

 the north-west Highlands come Silurian rocks 

 which are more or less metamorphosed. Up to 

 recent years geologists believed with Sir R. I. 

 Murchison that all the schists, &c., lying to the 

 east of the Cambrian and Archiean areas, and 

 extending down to the borders of the lowlands in 

 Strathmore, &c., were altered Silurian strata. 

 Probably this is the fact, but the work of the 

 < leolo^ical Survey in the north-west Highlands has 

 suggested some doubts. A line drawn from Stone- 

 haven to Helensburgh marks the southward range 

 of those schists and slates, &c. 



The Old lied Sandstone System (q.v.), consisting 

 of conglomerates, coarse and fine grained sand- 

 stones, and dark-coloured flagstones and shales, 

 with characteristic fossils of ganoid and placoid 

 fish, overlies the Silurian in several districts in 

 Scotland. Nearly all Caithness and the seaward 

 portions of Sutherland, Ross, Cromarty, Inverness, 

 Nairn, and Elgin, belong to these strata. A 

 broad band, extending on the east coast between 

 Stonehaven and St Andrews, stretches across the 

 country to Helensburgh and Dumbarton on the 

 west. The same strata appear again in Hadding- 

 ton, Berwick, and Roxburgh, in Lanark, and in 

 A\ i shire. Old Red Sandstone likewise occurs in 

 South Wales and the neighbouring English counties, 

 extending from the Silurian district to the Severn 

 and the Bristol Channel, and containing in a large 



basin the South Wales coalfield. The highly fowul- 

 iferoiiM strata of north Devon, and of Month Devon 

 and Cornwall (Devonian HVHtem) a'e believed to 

 l>e on the same geological horixon n- the old Red 

 Sandstone. They consist of slates, ind-i<.M--, 

 and linn-tun. -, and contain numerous coral- and 



shell fish. 



The Ciu-lioniferous System (q.v.) may 1* said to 

 occupy a broad tract extending from the Bristol 

 Channel to the base of the Cheviots. The strata 

 are not continuous between these limit-, but are 

 broken up in some places by the appearance on 

 the surface of older strata, while in others they are 

 covered by newer deposits. The various detached 

 coalfields are (1) the South Wales, in Glamorgan 

 and Pembroke ; (2) the Bristol, and (3) the Forest 

 of Dean, in Gloucester ; (4) the Forest of Wyre, in 

 Worcester; (5) Shrewsbury, and (6) Coafbrook- 

 dale, in Shropshire; (7) north and (8) south 

 Staffordshire ; (9) Warwickshire; (10) Leicester- 

 shire; (11) Flint and Denbigh; (12) Lancashire; 

 ( 13) York and Derby ; ( 14) Cumlierland ; and ( 15) 

 Northumberland and Durham. In the northern 

 portion of this great tract of carboniferous strata, 

 where the millstone grit and carlxmiferous limestone 

 are largely developed, few seams of coal of any 

 value are contained. The limestone in Derby is 

 rich in metallic ores. The carboniferous strata of 

 the north of England extend beyond the Cheviots 

 into Scotland, forming a narrow band from the 

 Solway to the North Sea, in the counties of Dumfries, 

 Roxburgh, and Berwick. The only coalfield in 

 this district is one of small extent at Canonbie, in 

 Dumfriesshire. The carboniferous strata in Scot- 

 land, with the exception just stated, are confined 

 to the immense trough between the Silurian and 

 Old Red Sandstone systems on the south and the 

 Old Red Sandstone on the north, which is com- 

 pletely occupied by them, except where underlying 

 older strata rise to the surface. Considerable 

 tracts of sandstone and limestone without coal 

 break up the coal-bearing beds into the following 

 coalfields : the Midlothian, the Fife, the Lanark 

 and Stirling, the Ayrshire, the Sanquhar in Dum- 

 friesshire. Beside coal, the whole of the carbonifer- 

 ous series contains immense stores of argillaceous 

 carbonate of iron, from the ore of which is produced 

 the great bulk of the iron used in the country. 

 The sandstones of this period form beautiful and 

 durable building-stones, the limestones are of great 

 commercial value, and many of the less indurated 

 shales are good fireclays. 



The Permian System (q.v.), consisting of magne- 

 sian limestone and sandstone coloured with oxide 

 of iron, occupies a considerable area in Durham, 

 and borders the carboniferous rocks in Dumfries, 

 Cumberland, Westmorland, Lancashire, Cheshire, 

 Shropshire, Stafford, Worcester, Warwick, Not- 

 tingham, and York, and in Glamorgan. The sand- 

 stone is quarried for building. 



The typical triple series of the Triassic System 

 ( q.v.) occurs in Germany; the British representatives 

 consist of variously -coloured sandstones and marls. 

 They occupy a considerable surface in Lancashire, 

 Cheshire, Shropshire, and Stafford, and extend as a 

 ribbon of varying breadth, from the mouth of the 

 Exe, through Devon, Somerset, Gloucester, Wor- 

 cester, Warwick, Leicester, Nottingham, York, and 

 Durham, to the coast at Hartlepool. The only 

 deposits of rock-salt in Britain occur in the Toassic 

 jocks of Cheshire and Worcestershire. 



The Jurassic System (q.v.) is composed of an 

 extensive series of limestones, marls, sandstones, 

 and shales, which stretch in a broad belt from 

 Yorkshire to Dorsetshire, passing through Lincoln, 

 Worcester, Warwick, Northampton, Huntingdon, 

 Bedford, Buckingham. Oxford. Gloucester, and 

 Wilts. The best building materials in England 



