70 Transactions. 



NOTES ON A GLACIAL DEPOSIT NEAE THOENHILL, 



By Joseph Thomson. 



Eead January 4th, 1878. 



During the formation of the branch railway line to 

 Gatelawbridge Quarry from Thornhill Station, a deposit of a 

 peculiar character was exposed in one of the cuttings. As 

 far as can be gleaned from the Memoirs of the Geological 

 Survey nothing similar occurs in Dumfriesshire, and — if my 

 inferences be true — it will be found that a very important 

 page of the later geological history of this country has been 

 revealed by its discovery. This breccia — for so we may term 

 it, as being both convenient and applicable — is overlain by a 

 deposit of ordinary boulder clay, which covers all the sur- 

 rounding country, and as a description of the characters of 

 tho latter will serve to bring out more prominently those of 

 the former, we may take them both into consideration. 



Extending along the east side of the Glasgow and 

 South-Western Railway there is a ridge of a somewhat 

 irregular contour which in Closeburn breaks up into gTeat 

 mounds and heaps, and which shades off towards Carron- 

 bridge. The greater part of it is composed of boulder clay, 

 having as a backbone or nucleus the glacial deposit which 

 forms the subject of this paper. The boulder clay has all 

 the ordinary characters of that deposit. It is unstratitied, 

 forming a loose unarranged mixture of all sorts of materials 

 derived from the neighbouring rocks. In one place it may 

 be pure gravel, in another sand, or both may be mixed with 

 clay. The drifted fragments of stone are principally grey- 

 wacke, together with Carboniferous sandstones, Penman 

 Porphyrites, and sandstones, or, it may be, even fragments 

 of the underlying glacial breccia. They are all derived from 

 local rocks ; the boulders vary in weight up to two or three 

 cwts., and are considerably rounded, polished, and striated- 

 This o-lacial accumulation occurs scattered over the whole of 

 Middle Nithsdale in confused heaps and mounds. Some six 

 mouths ago, while the ridge was being cut through near 

 Thornhill btaLion, a rock differing in many important 



