946 “DR ROBERT CAMPBELL? ON 
Representative collections of boulders from these conglomerates at various horizons 
show that the boulders consist almost entirely of acid andesites and rhyolites. A big 
percentage of the former belongs to types found in the acid andesite zone of the 
Crawton group. None of the basic andesites or basalts are represented in the collections 
made from these conglomerates along the Highland Border. Sometimes the volcanic 
conglomerates are built up entirely of the debris of volcanic rocks, but more frequently 
they contain a small percentage of boulders derived from the Highland schist series— 
a point which is of interest in showing that the material was being derived from the 
area to the north of the Highland fault. Locally, too, there occur thin conglomerates 
of the “‘ Highland” type, but such form an insignificant part of the succession. The 
volcanic conglomerates are associated invariably with interbedded “tuffs.” While some 
of the latter may have been derived from an already consolidated series of lavas by the 
ordinary agents of denudation, numerous occurrences have been noted in which the 
sharply angular nature of the constituent fragments clearly shows that they are true 
pyroclastic tuffs. ‘These tuffs are rhyolitic rather than andesitic, and in this way 
differ from the tuffs associated with the Crawton group. LHxcellent examples occur’in 
the Bervie Water near the ford of Dillavaird, and in the Shag Burn opposite 
Honeybank. The tuffs are not separated from the volcanic conglomerates on the 
accompanying map, but they make up no inconsiderable part of the whole series. 
Indeterminable plant fragments, found in a thin intercalation of grey micaceous 
shales near the ford of Dillavaird, are the only fossils which have been noted in this 
part of the Arbuthnott group. 
D. The Garvock Group. 
This group consists for the most part of coarse “ Highland” conglomerates, with 
intercalated grits, sandstones, flagstones, shales, and limestone. It includes also the 
highest of the lava zones. 
The main belt of lavas extends from the North Esk near Marykirk to Cairn of Shiels. 
A minor group at a somewhat lower horizon occurs on either side of the Bervie Water 
near Whitefield, and a small development of lavas is found also to the north of 
Canterland Den, almost at the base of the Garvock series. The lavas are all basalts, 
oceasionally with phenocrysts of olivine, but more usually coarsely crystalline, non- 
porphyritic doleritic types. The slaggy surfaces show the usual “ sandstone-veining,” 
but the material of the veins in the highest flow at Balmakelly is a sandy limestone. 
The basalts give no evidence of having undergone contemporaneous erosion... This lava 
series does not appear in the northern limb of the Strathmore syncline, and, like the 
hypersthene-bearing series in the Arbuthnott group, thickens towards the south 
and east. 
In the coarse quartzite conglomerates of the group the boulders which occur in 
greatest numbers are flaggy gneisses. Quartzites and vein quartz also play an 
