82 PALAEOZOIC TIME. [CHAP, VI. 



near Milburn, where they are 700 feet ; northward they 

 rapidly thicken to over 2,000 feet, and southward they 

 increase to 1,800, and then to 2,500 at the head of the 

 Eden Valley. Along the border of the Lake District the 

 thickness of the same beds varies from 400 to 800 feet, 

 except at Mell Fell, where the basal conglomerates seem to 

 fill an old hollow ; north-west of Appleby they are about 

 900 feet, but south-eastward they gradually increase to 

 2,500 feet. 1 



Another ridge which was gradually submerged in Lower 

 Carboniferous times seems to have lain under Ingleborough, 

 and probably extended thence to the north-east. The total 

 thickness of the sub-Yoredale Beds near Ingleborough is 

 about 650 feet, of which 150 may be assigned to the basal 

 conglomerate ; while, to the north, the thickness near Sed- 

 burgh is 2,400, and to the west and south-west it is over 

 3,000 feet. 



With regard to the southern uplands of Scotland, it has 

 already been suggested that the western part of this region 

 was in connection with the Hiberno-Cambrian land, and we 

 have also seen that it probably supplied rock-fragments to 

 the conglomerates in the north of England ; but the great 

 valley through which the river Nith now runs seems to 

 have existed before the Carboniferous period, and to have 

 been occupied by a long gulf or inlet of the Carboniferous 

 Limestone sea, as testified by the fossils which occur in the 

 bands of limestone associated with the red sandstones and 

 shales of the Thornhill basin. The similarity of these 

 deposits to those of Ayrshire makes it probable that they 

 were continuous, and that the inlet was soon converted into 

 a strait which separated the upland region into two parts. 



The central uplands then became an island, and the red 

 sandstones and conglomerates which form the base of the 



1 For all these particulars I am indebted to Mr. Goodchild. 



