176 Professor W. Boyd DawJcins [June 6, 



of depression during whicli sandbanks and mudbanks were deposited 

 by water. The fact also that the coal-seams in a given sinking are 

 parallel, or nearly parallel, implies that they were formed on horizontal 

 tracts of alluvium, while the marine and fresh-water shells in the 

 associated sandstones and shales prove that they were near the level 

 of the sea, or within reach of a mighty river. This tract of forest- 

 clad marsh-lands, as Godwin-Austen and Prestwich have pointed out, 

 occupied the greater part of the British Isles, from the Highlands of 

 Scotland southwards as far as Brittany, and eastwards far away into 

 the valley of the Rhine, and westwards over the greater part of 

 Ireland. It swept round the hills of South Scotland and the Lake 

 district and the region of Cornwall. It occupied a delta like that of 

 the Mississippi, in which the forest-growths were from time to time 

 depressed beneath the water-line, until the whole thickness of the coal- 

 measures (7200 feet thick in Lancashire, 7600 in South Wales, and 

 8400 in Somersetshire) was built up. After each depression the 

 forest spread again over the sand and mud of the submerged parts, 

 and another peat-layer of vegetable matter was slowly accumulated 

 above that buried beneath the sand and mud. The great extent of this 

 delta implies the existence of a large river draining a large continent, 

 of which the Highlands of Scotland and the Scandinavian peninsula 

 formed parts, and which I have described before the Eoyal Institution 

 under the name of Archaia. 



3. At the close of the Carboniferous age, this vast tract of alluvium 

 was thrown into a series of folds by earth-movements. These have 

 left their mark in the south of England and the adjacent parts of 

 France, in the anticline of the English Channel, the syncline of 

 Devonshire, the anticline of the Mendip Hills and of the lower Severn, 

 and the syncline of the South Wales coal-fields. These great east and 

 west folds have been traced from the south of Ireland on the west, 

 through 35 degrees of latitude, through North France and Belgium, 

 as far as the region of Westphalia. Next, the upper portions of the 

 folds were attacked by the subaerial and marine agents of denudation 

 over the whole of the Carboniferous area, leaving the lower parts to 

 form the existing coal-fields which lie scattered over the surface of 

 the British Isles, and are isolated from each other by exposures of 

 older rocks ; and a broad east and west ridge was carved out of the 

 folded and broken Carboniferous and older rocks, extending from the 

 anticline of the Mendip Hills eastward through Artois into Germany, 

 and constituting the ridge or axis of Artois of Godwin- Austen. 



The next stage in the history of the folded Carboniferous and 

 older rocks is marked by the deposition of the Permian and Secondary 

 rocks on their eroded and waterworn edges, by which they were 

 partially concealed or wholly buried, and these newer strata thin off 

 as they approach the ridge of Artois. This barrier, also, of folded 

 Carboniferous and older rocks sank gradually beneath the sea in the 

 Triassic, Liassic, Oolitic, and Cretaceous ages, and against it the 

 strata of the first three named ages thin off, while in France and 



