462 TRANSACTIONS OF SECTION C. 
interbedded with fine red mudstones and made up mainly of fragments of the 
underlying (?) Upper Cambrian rocks. ‘The basement breccias rest uncon- 
formably on the (?) Cambrian. The unconformable junction, which is well seen 
on the north side of the headland at Ruthery Head, was formerly regarded as a 
line of faulting. 
2. About 20 yards east of Cowie Harbour there occurs a thick belt of grey 
and greenish mudstones and shales which yield Dictyocaris in abundance. From 
this horizon have been obtained also Ceratiocaris; Archidesmus, sp., and a new 
genus of Myriopod; (?) larval form of insect; Hurypterus, sp. noy. ; fragments 
of scorpion; plant fragments and worm-tracks. Further, a thin bed of reddish 
sandy mudstone underlying the above series has yielded numerous plates of a new 
Cyathaspis. 
3. About 60 feet below the Dictyocaris horizon there is a thickness of about 
40 feet of volcanic conglomerates and tuffs, the presence of which implies that 
the volcanic activity, which was so marked a feature in the history of this area 
during the Lower Old Red Sandstone period, had already been initiated in 
Downtonian times. 
Neither Dictyocaris nor Ceratiocaris has been found elsewhere in rocks 
younger than Upper Silurian, and, apart from the occurrence of tuffs, the litho- 
logical characters of the above succession recall at once the typical Downtonian 
rocks of the south of Scotland. The highest beds of the Downtonian pass con- 
formably up into the micaceous sandstone and conglomerates of Stonehaven 
Harbour, which may be considered as the base of the Lower Old Red Sandstone. 
II.—Oxtp Rep SANDSTONE. 
(a) Lower.—The Lower Old Red Sandstone series consists of a great thickness 
of coarse conglomerates and sandstones with intercalated lavas and tuffs. 
Palxontological evidence is everywhere meagre, but the recognition of a number 
of well-marked volcanic zones has been of value in elucidating the structure of 
the area. The lavas include dacite, hornblende-biotite andesites, augite ande- 
sites, hypersthene andesites, hypersthene basalts, and olivine basalts. The tuffs 
are all acid in character. Minor intrusions of presumably Old Red Sandstone 
age occur in the form of dykes and thin sills of quartz porphyry, biotite porphyry, 
dolerite, and lamprophyre. The distribution of the lavas indicates that the cen- 
tres of eruption lay along two lines—one to the east of the present coast-line, the 
other over the area of Dalradian Schists to the north of the Highland Boundary 
fault. 
The coarse conglomerates, which build up a great part of the succession, fall 
readily into two groups : (1) those in which boulders of quartzites or other ‘ High- 
land’ rocks predominate; (2) those which are made up almost exclusively of 
voleanic rocks—volcanic conglomerates. Two points of particular interest may 
be noted in the former group—the occurrence of boulders of the ‘ Haggis rock ’ 
type of greywacké, and the abundance of boulders of the ‘newer’ granites, 
which have been collected even from the lowest conglomerates. The distribution 
of the volcanic conglomerates points clearly to the denudation of a thick series of 
rhyolites and acid andesites which must have extended far to the north of the 
Highland fault. 
The chief structural feature of the Lower Old Red Sandstone area is a con- 
tinuation of the well-known synclinal fold of Strathmore. In Kincardineshire, 
however, in the district to the west of Elfhill, there intervenes between the 
syncline and the Highland fault a steep-limbed anticline, pitching out to the 
south-west. The southern limb of the syncline is traversed by numerous powerful 
dip faults. 
(b) Upper.—The Upper Old Red Sandstone occupies a small area on the coast 
in the neighbourhood of St. Cyrus. Although no fossils have been recorded, the 
lithological evidence—and particularly the occurrence of characteristic cornstones 
—leaves no room for doubt that here wé are dealing with an outlier of the more 
extensive tract of Upper Old Red Sandstone of Arbroath. In Kincardineshire 
the Upper Old Red Sandstone is everywhere faulted against the Lower, 
