Geology of Dumfries Basin. 217 



surrounded by the range of hills not very far off. This area is 

 encircled by the Kirkmahoe and Tinwald hills on the north and 

 east ; on the west by the Mabie, Terreg-les, and Dunscore hills ; 

 on the south by the Solway Firth, and is known as the "Dumfries 

 basin." (In this paper I only take in a part of the basin.) I may 

 remind you that the term " basin" in geology is applied to a 

 depression in the strata in which beds of later age have been 

 deposited. In this case the depression is in Silurian strata, 

 and the over-lying deposits of later age are Permian sand- 

 stone and breccia. In the Thornhill basin the Permian deposits 

 do not rest directly on Silurian strata as they do here. They 

 rest there on carboniferous strata, with associated volcanic rocks 

 — lava and tuff — so that the relations of the rocks there may be 

 said to be of a complex character, while here they are quite 

 simple. Of the rock' deposits we shall speak later on, and give 

 our attention in the first place to the superficial formation. 



The hill upon which we are supposed to have taken our stand, 

 and many other similar rounded elevations within the circle of 

 the hills on both sides of the Nith, are masses of boulder clay 

 or till. And not only are such elevations — drums or kames they 

 are called — but the greater part of the whole superficial deposits 

 of the district are also boulder clay. This formation attains its 

 greatest thickness in low-lying ground, thinning off as we ascend 

 valleys. It forms part of the '• moraine profonde " or ground 

 moraine which was formed and accumulated under the great ice 

 sheet which covered the land duiing the glacial period, as Green- 

 land is now covered. It covers a large portion of Scotland and 

 Ireland, and is found in England and Wales to the north of the 

 Thames and Bristol Channel. The appearance and character of 

 boulder clay varies in different districts, and is determined by the 

 character of the strata of the country over which the ice sheet has 

 moved. In this district it is brick red, the colour of the prevailing 

 sandstone, and from weathering within a few feet of the surface it 

 is loose and easily worked, but in tunneling at considerable depths 

 it is very much the reverse. In the excavation, some sixteen feet 

 deep, for the cellarage of the recently-erected Convent buildings a 

 typical section of boulder clay was exposed. It showed a mass of 

 tough unstratified clay, including smooth and glaciated boulders 

 (none of them very large), grits, greywackes, sandstone, and. 

 breccias, nests of gravel, and a large quantity of very fine sand, 



