J. G. Goodchild — Deutozoic Bocks of North Britain. 597 



part of Scotland at present under notice. To the north and north- 

 east of Dundee the volcanic rocks pass, by the thinning of the lavas, 

 into a series of alternately sedimentary and volcanic rocks — the 

 sediments in this case being, therefore, contemporaneous with some 

 of the volcanic rocks to the east. The confusion occasioned by 

 this feature appears to be further complicated by the anticlinal and 

 its accompanying fault just mentioned. It should be noted that 

 these volcanic rocks form a very conspicuous feature in the strati- 

 graphy of the Caledonian Old Red, and that they are usually present, 

 in some form or other, even when the lower beds and the upper 

 are entirely absent. 



The Caledonian Old Red volcanic rocks of Perth and Forfarshire 

 may well be several thousand feet in thickness where they attain 

 their fullest development. Sir Archibald Geikie (loc. cit., p. 1008) 

 further regards the volcanic horizon as occurring several thousand 

 feet below the highest beds of Strathmore, and also as being several 

 thousand feet above the base of the system. 



The volcanic zone certainly overlies a considerable thickness of 

 greywackes, flagstones, and mudstones, whose base has not been 

 seen. These lowest sedimentary beds, it may be here remarked, bear 

 a remarkably close petrographical resemblance to the type which 

 forms much of the Silurian rocks ; and it may be well to add that 

 the physical relationship of these Arbroath Flags (as they may still 

 be called) to the volcanic belt has not yet been quite clearly 

 made out. 



Turning now to the palaeontological evidence, it may be said that 

 very few fossils have yet been obtained from the higher parts of the 

 Strathmore Sandstones ; so there is no evidence to prove that these 

 beds may not be contemporaneous with the very lowest subdivisions 

 of the Orcadian Series. Near the base of the Strathmore Sandstones, 

 and close to the top bed of the main part of the volcanic rocks, 

 occurs an upper fossiliferous band which has yielded myriapods 

 such as Kampecaris and Archidesmus, together with imperfectly 

 preserved plants, some of which have been referred to Psilophytiim 

 robustum; while at a slightly lower horizon, and contemporary with 

 some of the volcanic rocks, is the zone which has yielded the chief 

 Acanthodian fish remains. One of the best known of these 

 fossiliferous localities is at Tilliewhamland Quarry, Turin Hill, near 

 the town of Forfar. These rocks are there extensively quarried 

 for flagstones, and they have yielded fossils which have been cata- 

 logued by the late Mr. Powrie as follows : — MesacantJius mitchelli, 

 Ischiiacanthus gracilis, Climatius scutiger, C. uncinatus, G. reticidatus^ 

 Parexus recurvus, P. falcatus, Euthacanthus mitchelli, E. elegans, 

 JE. gracilis, E. curtus, Cephalaspis pagei, C. asper, Thelodus pagei, and 

 with Plerygotus angliciis, Stylonurus ensiformis, and also with Parha 

 decipiens, etc. Similar beds occur near this horizon at Farnell. 



The beds exposed at Turin Hill are on the north limb of the 

 great faulted anticlinal above mentioned. The axis of this anticlinal 

 ranges, roughly speaking, from near the confluence of the Earn with 

 the Tay, below Perth, through a point about midway between the 



