736 STRATIGRAPHICAL GEOLOGY. [Boor VI. 
confertifolia. The old genus Cyclostigna here disappears (C. minuta, 
Nathorstii). The more characteristic lepidodendroids are Lepidodendron 
weikianum, veltheimianum, squamosun; Knorria imbricata, acicularis. The 
flora includes also Stigmaria ficoides, rugosa ; Bornia transitionis: Astero- 
phyllites elegans, &c. 
§ 2. Local Development. 
The European development of the Carboniferous system presents 
certain well-marked local types which bring clearly before the mind some 
of the geographical features, as well as the succession of geological changes. 
During the earlier half of the Carboniferous period there still lay much 
land towards the north and north-west, whence a continuous supply of 
sandy and muddy sediment was derived. A sea of moderate depth 
and clear water extended from the Atlantic across the site of Central 
Treland, the heart of England, and Belgium into Westphalia. The 
southern margin of this ancient Mediterranean was probably formed by 
the ridge of older Paleozoic and crystalline rocks, which, extending from 
“the west of England into the Boulonnais, and from Brittany into 
Central France, sweeps eastward by the uplands of the Ardennes, 
Hundsruck, Taunus, and Thuringer Wald into Saxony and Silesia. In 
the deeper and clearer water massive beds of limestone accumulated ; 
but towards the land, at least on the north side of the sea, there was 
an increasingly abundant deposit of sand and mud, with occasional seams 
of coal and sheets of limestone. The whole region underwent slow 
subsidence and infilling of sediment, until at last vast marshes and 
jungles occupied tracts that had been previously sea. By degrees the 
lower parts of the surrounding land were likewise submerged beneath 
the accumulating coal-growths, which consequently spread over the 
sinking areas. Hence while across the central portions of the Carbon- 
iferous region the normal succession of strata presents a lower marine 
division consisting mainly of limestone, and an upper brackish-water 
division composed of sandstones, shales, and coal seams, the marginal 
tracts show hardly any limestone, some of them indeed, as in Central 
France, containing only the very highest part of the upper division. 
The British Isles.!'—This general sequence is well illustrated in the 
structure of the Carboniferous rocks of Britain—an area sufficiently 
extensive to contain more than one type of the system, and thus to cast - 
interesting light on the varied geographical conditions under which the 
rocks were accumulated. As the land whence the chief supplies 
of sediment were derived rose mainly to the north and north-west, 
while the centre of England and Ireland lay under clear water of 
moderate depth, the sea shallowed northwards into Scotland, and its 
bottom was covered with constantly accumulating banks of sand and 
sheets of mud. Hence vertical sections of the Carboniferous system 
of Britain differ greatly according to the districts in which they are 
taken. The subjoined table may be regarded as expressing the typical 
! Detailed information regarding British Carboniferous rocks will be found in the 
Memoirs of the Geological Survey. See also Phillips’ “Geology of Yorkshire,” Hull’s 
“Coal Fields of Great Britain,” and papers by Prestwich (Geol. Trans. 2nd ser. v.), Sedg- 
wick (Op. cit. ix., Q. J. Geol. Soc. viii., Proc. Geol. Soc. ii.), Binney (Q. J. Geol. Soe. ii. 
xviii.), Kirk by (Op. cit. xxxvi.), Green and Russell, “ Geology of Yorkshire Coalfield ” 
in Mem. Geol. Surv. 
