Paleo-Geological and Geographical Maps of the British Islands. 267 
' great lakes of Scotland and of the north of Ireland, bounded on all sides by meta- 
morphosed strata, were formed, while vast masses of material were accumulated 
over the region of the south-west of Iveland, but in this instance, probably under 
the ocean. 
Upper Siluruin Areas. 
The principal areas of this series are to be found along the eastern borders of 
Wales, extending from the north coast at Conway southwards through Montgomery- 
shire, Shropshire, Radnor, into Hereford and Monmouth. Isolated portions rise from 
below the South Staffordshire coalfield, as at Dudley. Eastwards these beds extend 
under the Cretaceous rocks, and have been proved by borings at Ware* in 
Hertfordshire, and no doubt, they extend eastwards to the coast. But in Belgium 
the Upper Silurian rocks are unrepresented, and the Devonian rocks lie in a trough, 
having the Lower Silurian beds of Brabant on the north, and the Cambrian beds of 
the Ardennes on the south, against the flanks of which the more recent strata were 
originally deposited.t As the “ Devono-Silurian ” beds are in all probability re- 
presented by the “Systtme Gedinnien” (in part at least) at the base of the 
Devonian Series, they are represented in Plate XXV. Fig. 1, and the sea area is 
extended over the north of France and Belgium, along the line of this old trough. 
The Upper Silurian beds lie along the southern flanks of the Cumberland 
mountains, having a southerly dip, and probably extend eastwards under the 
Carboniferous rocks to the coast. They again occur along the flanks of the 
southern uplands of Scotland, where they were probably separated from the 
sea, and towards the close of that epoch the area was converted into a lake, 
in which were deposited the beds of the Devono-Silurian series (Lower Old Hed 
Sandstone) near St. Abb’s Head. 
In Ireland, Upper Silurian Beds occur in Dingle (Kerry), passing upwards into 
the Devono-Silurian, or Dingle Beds ;{ they also occupy considerable tracts on both 
sides of Killary Harbour and the shores ot L. Mask ; and they are again found 
forming a small tract on the borders of Roscommon and Sligo. The areas of the 
Devono-Silurian beds have already been stated. 
Distribution of Land and Sea.—As will be seen by referring to the map (Fig. 2, 
Plate XXV.), the land areas of the region now under description lay both towards 
the north and towards the south, between which there was a gulf of moderate depth 
extending over the region of the south of Ireland, England, and the north of France, 
under which the marine strata were deposited. This gulf threw out an arm towards 
the north, but how far it stretched beyond the eastern coast-line it is impossible to 
say. The land area of the north was probably a prolongation of the Scandiuavian 
promontory, while large tracts of the Atlantic to the westward formed continuous 
. * Mr. R. Etheridge, F.r.s.,. The Times, 19th May, 1879. 
+ Dr. Mourlon, Géol. de la Belgique, t. 1, p. 54. t Expl. Mem. Geol. Survey, Sheets 160 and 170. 
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