398 G. Hicldinij — Old Red Sandstone of Forfarshire. 



treated in at least two distinct parts — the present one, dealing with 

 the rocks in Forfarshire, and a subsequent one in which I hope to 

 discuss the more general question. 



It would be impossible properly to realise the magnitude of the 

 unconformity in Forfarshire without a preliminary knowledge of the 

 general succession and tectonic structure of the Lower Old Eed series 

 in that locality. Notwithstanding the fact that the series is believed 

 to reach there a greater thickness than anywhere else in Britain, no 

 adequate description exists, and hence I need make no further apology 

 for the brief sketch which forms the first section of this paper. 



General Features of the Lower Old Red San^dstone. 



The counties of Forfar and Kincardine are sharply divided into 

 highland and lowland sections by the line of the great Highland fault, 

 running south-west from the coast at Stonehaven, and bringing down 

 the Old Eed to the south against the schists and granites on the north. 

 The Old Red underlies the whole of the lowland tract. Between the 

 foot of the highlands and the vallej' of the Tay the low ridge of the 

 Sidlaws intervene, with Strathmore between it and the highlands. 

 These physical features are directlj' related to the folding of the 

 subjacent rocks. Against the highland fault the sandstones and 

 conglomerates lean almost vertically. After a couple of miles or so 

 the dip rapidlj' becomes lower, and the S3'nclinal axis is reached, 

 which follows the line of Strathmore. South of the axis the dip in 

 the reverse direction increases to about 25'-'. It afterwards decreases, 

 and again changes its direction beyond the anticlinal axis which runs 

 along the Sidlaws. On the southern limb of the anticline the dip 

 again rises to about 25°. This pair of folds may be traced right across 

 Scotland, the axes remaining sensibly parallel to the highland fault 

 the whole way, pointing, no doubt, to the simultaneous production of 

 fault and folds. These folds have been familiar for three-quarters of 

 a century, having illustrated the terms * anticline ' and ' syncline ' in 

 Lyell's " Elements." There is, however, another, but much less obvious, 

 series of folds affecting these rocks, with axes running north and south. 

 The influence of these is usually slight, but about Stonehaven an anti- 

 cline of this series brings up rocks much lower than would otherwise 

 be exposed — the lowest, indeed, in the district. 



With each of the two series of folds just referred to there is a series 

 of faults associated, some of which are marked on the Survey map. 

 For the most part, however, these are small, and I do not think they 

 need further comment. 



Table of the Loicer Old Red cf Forfarshire. 



Edzell Shales PIOOO 



Arbroath Sandstone ... ... ... ... 1200 



Auchmithie Conglomerate ... ... ... 800 



Eed Head Series 1500 



Cairnconnan Series ... ... ... ... 2000 



Carmyllie Series ... ... ... ... 1000 



Dunnottar Conglomerate ... ... ... 5000 



Stonehaven Beds ... 1500 



14,000 



