14 SCIENTIFIC SURVEY OF ABERDEEN AND DISTRICT 
The metamorphics have been broken into time and again by igneous 
rocks which occupy a very considerable extent of the exposed surface of 
the area. The later igneous intrusions are dominantly acid—granites 
and their allies ; but there are also basic types—picrites, gabbros, norites 
and other varieties. ‘These latter are more restricted in distribution 
than the granites, occurring as isolated masses in upper Deeside, Donside, 
and especially in central and eastern Aberdeenshire (Belhelvie, Haddo, 
Maud, Insch, Huntly and elsewhere). The intrusions, acid and basic 
alike, are manifestly of different ages, and while much diversity of opinion 
exists as to the date of intrusion, and while no criterion is yet known by 
which the age in every particular case may be definitely established, the 
igneous rocks may be roughly grouped into an ‘ older’ and a ‘ younger ’ 
series. ‘The older are represented by an intrusion or series of successive 
intrusions antedating or accompanying the earth-movements that foliated 
the metamorphics; the younger by an intrusion or a succession of 
separate intrusions later on the whole than the folding movements. 
The granites show a great variety of types, not fully explained, though 
the variation may be due, in part, to incorporation of the material into 
which they were intruded. Contamination of igneous masses by the 
assimilation of pre-existing rock is most clearly exemplified in the case 
of the basic intrusions. The phenomena have been worked out in detail 
about Huntly and eastern Aberdeenshire by Prof. Read, and the area 
has become the most instructive in Britain for the study of this aspect of 
igneous activity. 
B. PaL#ozoic.—Of the ordinary piecone systems that form the 
geological ground-work of most other parts of Britain, the North-east of 
Scotland shows scarcely a trace. Perhaps it is all the more remarkable, 
therefore, that actual traces of most of them do exist—Cambrian, 
Silurian (?), Old Red Sandstone, Permian, Trias, Jurassic, Cretaceous 
and even Tertiary deposits have all been recognised. Most of these are 
of small size, many of them are not even proved to be in situ; but they 
are of considerable theoretical interest. 
Slaty rocks of Cambrian (or Ordovician) age, scantily fossiliferous and 
associated with pillow-lavas and radiolarian cherts, are exposed on the 
coast a mile north of Stonehaven, where they are faulted against the 
metamorphics along the ‘ Highland Border.’ 
They are succeeded southwards by a thick series of Downtonian 
(Upper Silurian ?) sediments, also fossiliferous, which merge imperceptibly 
into the normal Old Red Sandstone just opposite the town of Stonehaven. 
This section has been described in detail by Dr. Campbell of Edinburgh 
and rivals in interest the section along the Moray Firth already mentioned. 
Southwards from Stonehaven, the Lower Old Red Sandstone forms many 
miles of the coast, where massive conglomerates and interbedded lavas 
are sculptured into rugged cliffs that make a beautiful coast-section, 
scenically as well as geologically. Inland they form an open fold, the 
‘ Strathmore Syncline,’ which expresses itself superficially as the ‘ Howe 
of the Mearns.’ 
But the Old Red Sandstone appears to have covered at one time the 
whole of the North-east of Scotland, for remnants of the formation are 
