Carboniferous Period in East Scotland. 251 
‘physical conditions. Two distinctly marine beds crop out on the shore 
at Cockburnspath above the great series of sandstones with which the 
Seremerston Coals are associated. An oil-shale also occurs on the shore 
north of Cove Harbour which is well known in the Scremerston district. 
LIDDISDALE. 
The Fell Sandstones, representing the beginning of the period, can be 
traced westwards through Woodcock Air to the sea south of Criffel, where 
they are succeeded by alternations of truly marine limestones with shales, 
sandstones and coal seams. A volcanic zone occurs just over the top of the 
Fell Sandstones which can be traced from Langholm throughout the 
Larriston Fells. The famous Langholm “scorpion bed” occurs within this 
zone, and represents a salt-water lagoon with an estuarine lamellibranch 
fauna. The whole crustacea and fishes so well preserved may have been 
asphyxiated by volcanic exhalations. Interstratified with the ash which 
accompanies it, there is a thin bed of oil-shale and black chert. The silica 
of the chert is in all probability a diatom deposit due to the water being 
impregnated with soluble silicates from the tuff. The Fell Sandstones are 
overlaid by the Scremerston and Lowick coal-bearing rocks consisting of 
sandstones, shales, fireclay, coals, and thick beds of truly marine limestones 
the continuations of the same zones as those of Plashetts. It is evident that 
along this line we have the edge of the great sea in which the lower members 
of the Yoredale rocks of the North of England and the Carboniferous Lime- 
stone farther to the south were deposited, the conditions of deposit being 
exactly similar to that to be described. 
CARBONIFEROUS LIMESTONE OF SCOTLAND. 
During the deposition of the lower portion of the Carboniferous Limestone 
series, marine conditions similar to those existing in Liddisdale had crept 
northwards over nearly the whole of the East of Scotland, the only parts 
escaping being some small islands in what are now the Southern Uplands. 
Over the whole area the conditions were wonderfully alike. The series of 
deposits can be broken up into three groups, viz. (2) A Lower Limestone 
group; (0) Middle Coal and Ironstone group; and (c) Upper Limestone group. 
The lowest limestones are well within the Dibwnophyllum zone of 
Vaughan’s succession, while the upper limestones may represent part of the 
Millstone Grit of England. 
In the Lower group there is a well-marked rhythm in the sedimentation, 
doubtless marking successive pauses in the general movement of depression 
of the area. When the cycle is complete, a coal seam, marking a land 
