240 Proceedings of the Royal Physical Society. 
Belgium and mid England than farther north. In Scotland the portions of 
the country that had been more or less levelled up by the Upper Old Red 
Sandstone sediments formed a gently sloping plain that became subject to 
incursions of the sea, and only the older Paleozoic rocks of parts of the 
Southern Uplands, Pentlands, and of the Cheviots, that had not been covered 
up by them, stood out as islands and were not entirely enveloped till Upper 
Carboniferous time. Thus it happened that the lowest members of the 
Carboniferous strata were deposited conformably upon the sediments of the 
Upper Old Red Sandstone. At the same time there seems to have been a 
compensating elevation of a continental region towards the north-west, of 
which our area became the coastal belt. 
CALCIFEROUS SANDSTONE SERIES. 
The lowest great division of the Carboniferous strata in Scotland is known 
as the Calciferous Sandstone Series from the constant recurrence throughout 
it of limestones. The term originally included the Upper Old Red Sandstone 
of midland Scotland and part of the Scottish Carboniferous Limestone 
Series, but is now restricted to the lowest division of the Carboniferous 
system, which comprises (a) a lower or Cementstone Group, and (0) an upper 
or Oil-shale Group (Fig. 1). These two contrasted types of sedimentation 
are typically developed only in midland Scotland, but not over the whole of 
that area. 
(a) CEMENTSTONE GROUP. 
The rocks entering into this group vary considerably according to the 
area in which they have been deposited. In central Scotland what is known 
as the Ballagan type is most prevalent, and best shown in the Campsie 
district. Where typically developed, the rocks show a rythmical alternation 
of mudstones and muddy cementstone bands with occasional beds of calcareous 
sandstone. The cementstone bands are mostly a chemical deposit, though 
many of them contain remains of Ostracods and bivalve Phyllopods. Large 
concentric pisolites also occur occasionally, suggesting secretion through 
lowly plant agency. More or less gypsum is associated with the cement- 
stones, sometimes in layers, but more often in veins; while pseudomorphs 
after rock salt have been found in such strata, in Salisbury Crags, by Mr A. 
Macconochie. Specimens showing pseudomorphs after rock salt are exhibited 
in the Perthshire Naturalists’ Museum at Perth, obtained from the small 
outlier of Ballagan beds exposed in the railway cutting at Dron, a little to 
the south of Bridge of Earn. ‘This outlier is the only remnant of the 
Carboniferous system that is known to occur to the north of the Ochil Hills 
