DEVONIAN AND OLD RED SANDSTONK SYSTEM 231 



separate names for these lakes, calling the first Lake Cheviot, the 

 second Lake Caledonia, the third Lake Lome, and the fourth Lake 

 Orcadie. This view, however, is not sufficiently supported by the 

 facts, so far as the three southern areas are concerned ; the Lome 

 and Cheviot areas were probably only extensions or bays connected 

 with one large Caledonian lake basin, which may also have 

 stretched south-westward into the north of Ireland, for patches of 

 Old Red occur at the very southern end of the Kintyre promontory. 

 The northern area, on the other hand, exhibits a different set of 

 beds which contain a different fish fauna, so that there does seem 

 to have been a Lake Orcadie or at any rate a separate Orcadian 

 basin of deposition. 



In the central area the Lower Old Red Series is of great 

 thickness, but no middle division exists, and the Lower Series is 

 overlain unconformably by the Upper Old Red, which passes 

 conformably into the overlying Carboniferous Series. In the 

 Orcadian area there is nothing which can be identified as Lower 

 Old Red, but there is a great thickness of the Middle Series with 

 an abundant fish fauna, and some patches of Upper Old Red 

 resting unconformably upon the beds below. 



There is a further great difference between the rocks of the 

 two areas. In all the southern districts the sandstones are 

 interstratified with thick sheets of andesitic lava and beds of 

 volcanic tuff and agglomerate, giving proof of volcanic action on a 

 very large scale, and from many volcanic vents, throughout the 

 whole of the Lower Devonian epoch. In the Orcadian area, on 

 the contrary, no such volcanic rocks are found, so that the eruptions 

 do not seem to have continued into the time of the Middle Series. 



In the following account of the stratigraphic succession of 

 beds these volcanic materials will only be mentioned incidentally, 

 and for more information about them the student is referred to 

 Sir A. Geikie's Ancient Volcanoes of Great Britain (1897). 



Caledonian Region. The Lower Old Red Sandstone is most 

 completely developed on the northern side of the great central or 

 Lowland trough, and the beds are finely exposed in the cliffs of the 

 Kincardine and Forfar coasts. Until quite recently this series was 

 supposed to include all the red rocks visible in Kincardine, but as 

 stated on p. 163 the lowest set of beds must now be "egarded as 

 the highest part of the Silurian System. 



The base of the Old Red Sandstone is the massive conglomerate 

 which forms Downie Point near Stonehaven, and this is part 

 of a group of coarse sandstones and conglomerates to which 

 Mr. G. Hickling 17 has given the name of Dunottar Conglomerate 

 (see Fig. 78). These beds occupy a long stretch of coast-line which 



