328 report— 1879. 



urinated the physical geography of the Devonian Age, three elevated tracts of land 

 crossed the kingdom from west to east, and that there were mountainous regions 

 running northwards and north-westwards, including North Wales, Western Ire- 

 land, and much of the North Atlantic. 



The southern high land barrier passed somewhere in the direction of the Bristol 

 Channel, and then to the east and slightly to the south, having a somewhat definite 

 continuation with the Ardennes. The central harrier, or high land, passed from 

 Shropshire eastwards by Leicester, and then to the coast; and the northern 

 was formed by hills in the present Lake district, extending eastwards. On the 

 south of the southern high land, the marine Devonian accumulated in a coral sea, 

 and to the north of it and between it and the central barrier the Old Eed lakes 

 obtained their water supply and sediment from the AVelsh hills of the period. 

 North of the central barrier interrupted lakes and land occurred and also to the 

 north of the northern barrier. The dry land and the barriers and hills were formed by 

 sub-rocks of Silurian and Cambrian age. 



There is no evidence to indicate that the southern barrier was of great height at 

 the end of the Devonian period, but there is some which points out that the first 

 physical change which initiated a new aspect of nature— the Carboniferous— was 

 a general subsidence of the region. The coral reefs sank below the bathymetrical 

 zone of the composite forms, and the sea breached the barrier. The southern Old 

 Eed lake began to have its waters impregnated with salt, and its great ganoid fish 

 were replaced by the cestraciont sharks of the age. These left their remains in 

 the bone bed at the base of the lower limestone shales, which are the earliest of the 

 Carboniferous series there. The irruption of the sea appears to have taken place to 

 the north of the central barrier also, and the subsidence was great there, a limestone 

 with some sandy strata forming gradually. In the north and north-east, in the 

 present district of the Tweed, deposits collected in shallow water, and vege- 

 tation grew which formed the coals at the base of the great Scour limestone. 



On the same and on slightly higher horizons are the coals of Fallow Field, 

 Tindall Fell, and Heskett. These are the earliest evidences of the Carboniferous 

 vegetation, and it was doubtless in full vigour whilst marine conditions existed to 

 the south. 



Probably the high lands constituting the barriers were not covered during the 

 subsidence, which permitted the accumulation of the marine deposits of the Car- 

 boniferous limestone age. For close to the coal-fields near the central barrier, 

 and which rest on upper Silurian rock, borings here found the remains of Car- 

 boniferous plants on the palaeozoic rock without the intervention of any sediments. 



Now the depth of the deposit of limestone about this central barrier is great, 

 and the question arises how was it produced in the immediate proximity of land 

 which was not covered by sea, and which does not appear to have sunken con- 

 temporaneously with the sea floor close by ? Sinking along definite lines bounded by 

 faults, is the only means by which this can be explained ; and this suggestion, which 

 was a favourite topic with Phillips, is all the more probable, when it is remem- 

 bered that the area of accumulation to the north of the barrier was one of vast 

 subsidence during the consecutive ages of the grits and coal measures, whilst there 

 was land still further north. If the stability of one and the instability of the 

 other are not conceded, the original height of the barriers must have been stupendous 

 and beyond example, so far as the size of their bases is concerned. 



There are many examples of what I resolved to call in a presidential address 

 before the Geological Society areas of comparative instability and which relate 

 apparently to radial upheaval subsidence along long lines of country where move- 

 ment has been rare. An instance on the grandest scale is seen in the history of the 

 Himalayas in relation to the peninsula to their south and south-west. For whilst 

 this last area was land during a vast age, that of the Himalayas was repeatedly a 

 marine tract, and suffered subsidences and elevations. 



Still further north and beyond the northern barrier, in the Scottish area, 

 Carboniferous plants lived a little later, and after a subsidence which permitted the 

 lower Calciferous series to accumulate. The lowest coals of the basin of the Clyde 

 are of this age, and the accompanjing clay, ironstone, and the fresh water limestones 



