598 J. G. Goodchlld — Deutozoic Rocks of North Briiain. 



towns of Dundee and Forfar, and tbence in the direction of 

 Montrose. Hence the fossiliferous horizon repi"esented at Turin 

 Hill is repeated to the south of the line mentioned. 



At a geological horizon lower still, as at Auchtertyre, near Newtyle, 

 in Forfarshire, but still above the main mass of the lavas, occurs 

 a bed which has yielded Cephalaspis lyelli, Fteraspis milchelli, and 

 some few Acanthodians. 



Furthermore, at what I take to be still lower fossiliferous horizons, 

 occur the beds of Carmylie, which have yielded most of the finest 

 specimens of Eurypterids obtained from Forfarshire. Acanthodians 

 of the types occurring at Turin Hill are found with these, as is also 

 Parka decipiens. 



What appear to be the lowest fossiliferous horizons occur at 

 Myreton, Tealing, and Leoch. 



The general biological facias of these Caledonian Old Red fossils 

 indicates, according to Dr. Traquair, a formation of an earlier date 

 than the Orcadian Old Red. This view of the relative positions of 

 the Caledonian and Orcadian Old Red formations has now again met 

 with general acceptance, and it will probably never again be called 

 in question. 



1'he volcanic rocks which have just been mentioned as giving rise 

 to the most prominent features of the Caledonian Old Red in the 

 Ochils and the Sidlaw Hills present physiographical features of 

 even more strongly-marked character in the Pentland Hills, in Glen 

 Coe, and also in the neighbourhood of Oban. The Cheviot Hills, 

 again, owe much of their physiographical character to the presence 

 of these rocks. St. Abb's Head, and some other places near that 

 part of the Scottish coast, also consist of andesitic lavas and tuffs of 

 the same age as those of the Pentland Hills and the Ochils. Here 

 and there at several localities south of tlie Firths of Forth and 

 Clyde the older sedimetitary rocks below tlie volcanic zone are to be 

 seen. As a well-known locality where such is tlie case may be cited 

 the beautiful river-gorge in which are situated the Falls of Clyde. 

 More generally, however, these sediments are absent, and the 

 volcanic rocks form the lowest member of the series, and these may 

 lie, often with a violent unconformity, upon any rock older than 

 themselves. 



Most of the granite bosses of the southern half of Scotland, and 

 perhaps nearly all of those in the north of England, appear to have 

 originated in connection with the volcanoes from which these 

 Caledonian Old Red andesitic lavas and their associated dykes of 

 Elvan and Porphyrite have been erupted. Where these Granites 

 and Porphyrites occur we may, therefore, expect to meet at no great 

 distance with remains of their related volcanic rocks. 



Leaving these details, however, for reconsideration presently, we 

 may now go on to consider the nature of the physical relation of the 

 Caledonian Old Red to the rocks next older in the series. So far 

 from graduating downward into the Silurian rocks, the local base of 

 the formation under notice lies with a violent unconformity upon all 

 of these rocks, and may repose indifferently upon Silurian, Ordovician, 



