The Geological Features. 157 



These four groups, as we have them east of Craig- 

 millar, form an immense basin, the northern side of 

 which is cut off by the sea. On the opposite or 

 Fife shore the strata again appear, and much in the 

 same order. Above the Carboniferous system no 

 rocks of a later date occur in the district — nothing, 

 in fact, till the deposits of the Glacial Period, 

 namely, boulder-clay and drift accumulations. 



The Igneous Rocks of the district present a very 

 striking appearance in the landscape — Arthur's Seat, 

 a volcanic neck, with the basalt plug forming its 

 apex, probably of early Carboniferous age ; and the 

 high mural escarpment of Salisbury Crags, consisting 

 of dolerite ejected between strata of the Calciferous 

 Sandstone. This bed, as well as that known as the 

 St Leonard's Crag, were both ejected late in the 

 geological scale, and belong to Tertiary times. These 

 bold escarpments afford most important evidence of 

 the denudation of the district, with the characteristic 

 " crag-and-tail " of the different prominences, such 

 as the Castle Rock of Edinburgh, the Calton Hill, 

 and Salisbury Crags. The igneous rocks of the 

 Pentlands very probably had their origin during Old 



