XXX. GEOLOGY OF DUMFRIESSHIRE. 



territory are measured by thousands of feet. When, however, we examine 

 the successive reappearances of the black shale series between Moffat 

 and the Dalveen Pass, the Birkhill shales gradually disappear, bemg 

 represented by thin dark blue shales with a few characteristic Birkhill 

 graptolites. Passing still further to the north-west, beyond the limits of 

 the Llandovery area, the Barren Mudstones are represented by grey 

 sandy shales with lenticular bands and nodules of limestone. Grey- 

 wackes, grits and conglomerates, yielding Caradoc fossils, appear ; and, 

 in the northern part of the county, overlie the (ilenkiln-Hartfell black 

 shales. Proceeding still further to the north-west, towards the county 

 boundary, west of Sanquhar, the higher zones of the Hartfell black 

 shales disappear, and the lower zones of this division occur as dark 

 seams in grey sandy shale. Taking these facts into consideration, it is 

 evident that the old land surface from which the sediment was derived 

 lay to the north-west. This conclusion receives support from the 

 occurrence of pebbles of crystalline schists from the Highlands, in some 

 of the Caradoc and Llandovery conglomerates, along the northern por- 

 tion of the Silurian tableland. 



The volcanic rocks underlying the Radiolarian cherts consist mainly 

 of contemporaneous lavas and agglomerates, with occasional masses of 

 intrusive dolerite and gabbro. They come to the surface along sharp 

 anticlines in the northern part of the county ; the extent of the ex- 

 posures depending on the breadth of the anticline and the depth to 

 which they have been cut by denudation. They are visible near 

 Wanlockhead, in the tributaries of the Euchan water, and on Bail Hill, 

 north of Sanquhar. The volcanic rocks underlying the cherts are not 

 met with in the Moffat area, because the various folcis have not been 

 denuded deep enough to expose this horizon. Volcanic tuffs are, 

 however, associated with the cherts and barren mudstones at certain 

 localities. 



The various bands of black shales in the Moffat area are succeeded 

 by greywackes, grits, conglomerates, and shales of T,landovery age 

 (Queensberry grits and Hawick rocks), occupying a broad belt of 

 territory. A line drawn from the Dalveen Pass south-westwards by 

 Moniaive to the county boundary near Casdefearn marks the northern 

 limit of this formation. To the north of this line they are underlain by 

 the Caradoc and Llandeilo rocks, while towards the south of Eskdale- 

 muir they pass conformably upwards into the Wenlock beds. In the 

 Moffat region there is no difficulty in drawing the base line of the 

 Llandovery formation, as it is everywhere indicated by the Diplograptus 

 acuminatus zone of the Lower Birkhill shales. The northern boundary 

 line from Dalveen Pass to Moniaive is rather uncertain, owing to the 

 disappearance of most of the well defined Birkhill zones. Though 

 Llandovery rocks occupy a wide area, it is evident that their thickness 

 is not excessive, because the same beds are constantly repeated by 

 folding. In the central area, the dominant types, consisting of massive 



