TRANSACTIONS OF SECTION C. 685 



Ingleborougli by ahing-le resting- on eroded reefs of older rocks a few feet thick. 

 They form a band running from the north-east to the south-west on the northern 

 boundary of the central valley of Scotland, and re-appear in the same line on the 

 Hanks of the mountains of Donegal in Ireland. From this point they sweep south- 

 wards by the hills of Connaught and Kerry, where they are lost in the Atlantic. 



They mark the coastline of Archaia as'ainst which the sea beat at the beginning 

 of the Carboniferous period. From this coastline Archaia extended over the 

 ■waters of the Atlantic indefinitely to the north acd to the west. 



The sea to the south was studded with islands, each marked bv the shingle- 

 beaches, the two South Scotch Islands, the Island ofCumbria and of Man, and in 

 Ireland of Mourne and of Wicklow. In North Wales the Lower Carboniferous 

 shingle beds, sand, and mudbanks sweep from the valley of the Conway eastwards 

 and southwards to Llangollen in the direction of Shrewsbury, and in South Wales 

 from St. David's and Pembroke in the direction of Hereford. From these points 

 the coastline is either obliterated or concealed by newer rocks; the land, however, 

 was certainly continued eastward, so as to include the areas of South Stafford- 

 shire, Warwickshire, and Cliarnwood Forest, in Leicestershire, as Jukes pointed 

 out, and has repeatedly been struck in deep borings for coal, which prove the 

 absence of the Lower Carboniferous rocks. For this tract of land the term 

 * Middle Island ' is proposed. It probably extended westwards so as to include 

 the Wicklow Mountains. Its eastern boundary is concealed. Land also existed 

 at this time in Cornwall, and extended westwards to include the Scilly Islands, 

 and to the south-east across the Channel in the direction of the mouth of the Seine, 

 and southwards over Normandy and Brittany. This land, as Bonne}- has pointed 

 out, constituted a lofty mountainous tract during the later primary ages, barrino- 

 the waters of the Atlantic from those of the Lower Carboniferous Sea to the east! 

 It may conveniently be termed the South-British land, because it not only includes 

 Cornwall, but also Normandy and Brittany. Whether it was an island, or whether 

 it was connected with the tnassifoi Archaia to the west, is an open question. 



While these littoral accumulations were being formed on the margin of the 

 land the British area was gradually but unequally sinking, and the waters in the 

 area of Derbyshire became sufficiently deep and clear to allow of the formation of 

 no less than 5,500 feet of limestone. This ' mountain ' or Carboniferous limestone 

 thins oif from this point in every direction. To the north in Durham and North- 

 umberland and in the central valley of Scotland it is broken up by sandbanks and 

 mudbanks, and becomes a subordinate division in a coalfield. To the south in like 

 manner it alters its physical characters as it approaches Middle Island, in Flint and 

 Denbigh, and it is abruptly brought up by the land in the areas of South Stafford 

 and Charnwood, On the southern shores of Jliddle Island it is reduced in 

 Pembrokeshire, according to Ramsay, from a thickness of 2,500 feet to nothing in a 

 distance of 12 miles. 



During the accumulation of the Yoredale sandbanks and mudbanks the sea 

 was becoming more and more shallow until in the time of the Millstone Grit it 

 was mainly occupied by littoral deposits. These two divisions in North Lancashire, 

 in Pendle Hill, are no less respectively than 4,675 and 5,500 feet. 



We may learn from the study of the isolated coalfields that the great hori- 

 zontal tract of forest-clad alluvia which constitute the Coal-measures occupied 

 nearly the whole area of the British Isles in the Upper Carboniferous age from 

 the Scotch highlands southward, the dead flatbeingbrokenonly by the higher lands 

 — the old islands of the Lower (Carboniferous Sea — which I have already described. 

 They were formed in, indeed, a delta of a mighty river analogous in every particular 

 to that of the Mississippi — a delta in which, from time to time, the forest growths 

 became depressed beneath the water until the whole thickness (7,200 feet in Lanca- 

 shire) was accumulated of coal seams and associated sandstones and shales. After 

 each depression the forest spread again over the bare expanse of sand and mud 

 piled up in the submerged area. In this manner we can account for the fact that 

 there is scarcely any, if anj^, change to be noted in the flora during the great length 

 of time implied by the great thickness of the Carboniferous strata. 



The enormous extent of the Upper Carboniferous delta implies a river of great 



