450 THE FEESH-WATER LOCHS OF SCOTLAND 
the Lower Carboniferous rocks of Linlithgowshire. The highest 
subdivisions of the system occupy the centre of the basin, and the 
lower members crop out round the margin in normal order, except 
where the regular succession has been disturbed by faults. The same 
features are displayed in the Midlothian and Ayrshire basins. 
The beginning of the Carboniferous period was characterised by a 
remarkable outburst of volcanic activity, whose relics now form 
prominent topographical features in the country. In Haddingtonshire 
they form the Garleton Hills ; in Midlothian they are to be found in 
Arthur's Seat, Calton Hill, Craiglockhart, and at Corston, south of 
Mid-Calder. They sweep in a great semicircle from Stirling along 
the Campsie and Kilpatrick Hills to the Clyde at Bowling, thence 
by the Renfrewshire Hills and Gleniffer Braes to the high grounds 
near Strathaven — a distance of 70 miles. Still farther west, they 
give rise to prominent features in Bute, the Cumbraes, Arran, and in 
Kintyre. Beyond the Silurian tableland they constitute a belt of 
ground curvincr round the west side of the basin of Lower Carbon- 
iferous rocks in Berwickshire and Roxburghshire, and near the Border 
territory they can be followed continuously by Langholm and 
Birrenswark to Annandale. The lavas belonging to this period of 
vulcanicity consist mainly of various types of basalt, and more acid 
varieties comprising mugearites and trachytes. An interesting feature 
connected with these extrusions is the number of orifices still to be 
found, representing the vents from which the materials were dis- 
charged. They are usually arranged in a linear manner, and are now 
filled with basalt, trachyte, and volcanic agglomerates. 
The Carboniferous formation as represented in Scotland may be 
arranged in four great divisions : — (1) the Calciferous Sandstone series 
at the base ; (2) the Carboniferous Limestone series ; (3) the Millstone 
Grit ; (4) the Coal Measures. 
The Calciferous Sandstone, when typically developed in the Central 
Lowlands, comprises two subdivisions : (1) the Cementstone group ; (2) 
the Oil-shale group, the latter passing upwards into the Carboniferous 
Limestone series. The lower subdivision, typically represented at 
Ballagan, near Strathblane, is composed of grey, blue, and red shales 
and clays, white or yellow sandstones and cementstones, from which 
fragments of plants and fish scales have been obtained. The deposits 
in the Central Lowlands seem to have been laid down under estuarine 
or lagoon conditions ; but on the south side of the Silurian tableland 
alono; the Scottish Border marine bands occur in the strata now 
grouped with the cementstones, thereby implying incursions of 
the sea. 
The overlying Oil-shale group consists of grey, blue, and black 
shales, oil-shales, thin bands and nodules of clay-ironstone, limestones, 
