LAKES m RELATION TO GEOLOGICAL FEATURES 449 
recognised this divergence as represented in Caithness, and referred 
the flao'stone series to the middle division of the Old Red Sandstone — 
a view which has been strengthened by the researches of Dr Traquair 
in recent years. In that county, conglomerates and sandstones occur 
at the base, and graduate upwards into grey and blue bituminous 
flagstones charged with fish-remains, and succeeded by the sandstones 
and flags of John o' Groats. On the other hand. Sir A. Geikie 
contends that the Orcadian series north of the Grampians are the 
equivalents in time of the Lower Old Red deposits south of that chain. 
He further holds that the admitted palajontological distinctions 
between the two areas are probably not greater than the contrast 
between the ichthyic faunas of adjacent but disconnected water basins 
at the present time. 
The Upper Old Red Sandstone everywhere rests unconformably on 
the older rocks, but graduates upwards into the Carboniferous forma- 
tion. The nature of this unconformability clearly shows that the 
members of the lower division, including the volcanic rocks, were 
elevated, folded, and subjected to extensive denudation before the 
deposition of the Upper Old Red strata. In places valleys or hollows 
were excavated in the Silurian tableland during this period of erosion. 
The strata consist of conglomerates, sandstones, marls, and corn- 
stones, from which a characteristic assemblage of fish-remains has been 
obtained. North of the Grampians they appear in the coastal belt 
of Elgin and Nairn, in Caithness, in the island of Hoy, and in Shet- 
land. They usually form a fringe round the basal beds of the 
Carboniferous system in the Central Lowlands and along the southern 
flanks of the Silurian tableland. 
CARBONIFEROUS 
The records of the Carboniferous formation are of great im- 
portance. The succession of sandstones, shales, limestones, coals, and 
ironstones composing this system have been carefully studied, owing 
partly to their economic value, and partly to the rich fauna and flora 
embedded in the rocks. Scotland possesses a large development of 
these rocks, though owing to subsequent folding and denudation 
they have been confined mainly to the Central Lowlands and the 
Border territory. The detailed examination of the Carboniferous 
areas shows that the strata are arrancred in a series of basins much 
intersected by faults ; the crests of the anticlinal folds being occupied 
by the lower subdivisions of the formation, or by rocks of older date. 
One of the best examples of this disposition is the great Lanarkshire 
basin, which is bounded on the north by the Campsie Fells, on the 
west by the Renfrewshire and Eaglesham Hills, on the south by the 
Old Red Sandstone of Lesmahagow and Lanark, and on the east by 
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