16 SCIENTIFIC SURVEY OF ABERDEEN AND DISTRICT 
about twenty miles north of Aberdeen—have been found to contain 
ice-worn Pliocene shells ; and near Fyvie (at Windyhills) and Turriff 
(at Delgaty) in central Aberdeenshire, as also along the high ridge eastward 
from Ellon, there occur considerable spreads of post-Cretaceous gravels 
(with flints derived from the Chalk), They are not river-gravels, they 
cannot be shown to be glacial, and are referred (with some hesitation) to 
the Pliocene. Rocks of Pliocene age (Coralline Crag) are known, probably 
in situ, on the floor of the sea east of the Orkneys. 
Fragmentary as these deposits are, they are yet eloquent of the changes 
that the North-east of Scotland has seen since Old Red Sandstone times. 
The history of the North-east becomes more detailed and consecutive 
again as Tertiary time merges into the Quaternary, which is dealt with 
in the article that follows. 
II. SURFACE GEOLOGY. 
BY 
ALEX. BREMNER, M.A., D.Sc., F.R.S.E. 
A. DEVELOPMENT OF RIveR SysTEM.—The theory of Mackinder, 
adopted for Scotland by Peach and Horne, that Scottish rivers originated 
on a peneplain, elevated in Early to Mid-Tertiary times and tilted towards 
the south-east, requires modification. North of the latitude of Inverness 
the original drainage lines did run north-west and south-east ; elsewhere 
in Scotland they followed west to east lines, e.g. the through-valleys west 
of the Great Glen, the Leven-Blackwater-Tummel, Earn, Forth (according 
to Cadell), Tweed, and the Solway-Tyne river. The peneplain, which 
included most of the British area, was warped during elevation (particularly 
along old lines of weakness) and its slope varied from one region to 
another ; at later dates, too, there occurred slight movements both of 
subsidence and elevation, e.g. the uplift that rejuvenated the lower Spey. 
In the area under discussion the older rocks of the tilted peneplain 
must have been largely swathed in a mantle of Middle Old Red Sandstone, 
with probably younger rocks including some deposits of Cretaceous age : 
the widely distributed outliers of Old Red are very suggestive. The 
Tertiary drainage lines were therefore established on an east-sloping 
surface mainly of Old Red Sandstone. 
Rivers in course of time cut through the weak, unmetamorphosed 
sedimentary cover and became superimposed on the more resistant, 
metamorphic Highland Schists which the valleys marking the older lines 
of drainage now cross regardless of structure. 
Of older lines of drainage the most evident are (1) the well-marked, 
winding hollow, roughly parallel to the Moray Firth coast and extending 
from north of Binn of Cullen to Boyndie Bay ; (2) the transverse valley 
running from Mulben (Rosarie Burn) by Keith to Rothiemay (Isla) and 
Turriff (Deveron) and thence in a gentle S-bend by the Idoch Water 
and Ugie to near Peterhead ; (3) the hollow passing from Cabrach by 
