12 SCIENTIFIC SURVEY OF ABERDEEN AND DISTRICT 
III. 
GEOLOGY 
GEOLOGICAL boundaries ignore the limits of counties and parishes ; but 
for present purposes it will be convenient to treat the Aberdeen area as 
comprising, mainly, the counties of Elgin, Banff, Aberdeen and Kincardine. 
The bed-rock within this area, while adequately exposed, is widely 
blanketed by sheets of glacial drift and incoherent deposits of recent 
date. The geology, therefore, falls naturally into two divisions : 
I. The foundation rocks, or SOLID GEOLOGY ; 
II. The overlying loose deposits, or SURFACE GEOLOGY. 
With the latter may be included a consideration of the agencies that 
have moulded relief and influenced scenery. 
I, SOLID GEOLOGY. 
BY 
Pror. A. W. GIBB, M.A., D.Sc., F.R.S.E. 
The most notable structural feature is the line of fracture known as 
the Highland Fault, which, cutting across Scotland from west to east, strikes 
the coast-line near Stonehaven and divides the district under consideration 
into two sharply contrasted geological areas. South of the fault lie 
normal sediments of Old Red Sandstone and younger age ; north of it, 
and sweeping westwards towards the Spey valley, lie masses of more 
ancient crystalline rocks. These older rocks are in places overlain by 
undenuded fragments of younger systems. The several formations may 
be briefly considered in order of age. 
A. Pre-CaMBRIAN.—The oldest rocks and the most widespread are 
metamorphic rocks. Of the three groups of rocks, of indefinite age, 
that occupy the greater part of Scotland between the Caledonian Canal 
and the Highland Fault—the Moines, the Dalradians and the small 
group sometimes called Lennoxians—those of the North-east are usually 
regarded as Dalradians. ‘That is to say, they are the same rocks as 
those of the Central Highlands of Scotland. They have the same 
N.E.-S.W. trend and, lithologically, they have a general resemblance 
to the typical groups of Perthshire. They are now gneisses, mica- 
schists, quartzites, slates, etc., but they were once normal sediments, 
sandstones, clays, limestones; they contain also abundant igneous 
intrusions. Even in their metamorphosed condition they frequently 
retain their old bedding planes and other features characteristic of 
sediments. One significant feature they lack: they have been searched 
