G. HicJding — Old Red Sandstone of Forfarshire. 403 



Uppek Old Red Sandstone. 



The main mass of this deposit, in. JN'orthern Fife and the Carse 

 of Gowrie, has been several times described, most recently by- 

 Sir A. Greikie in his " Geology of Western Fife and Kinross " (A. Geikie, 

 1900), and therefore needs no further description here. The small 

 outliers, however, along the coast of Forfar and Kincardine have never 

 received attention. 



• There are four of these patches, which obviously represent the 

 remnants of a once continuous strip along the shores. The most 

 southerly is near Arbroath, the next forms the tiny promontory called 

 Boddin Point, at the north end of Lunan Bay, while the third (which 

 is largely covered with alluvium) and fourth form a broken strip from 

 the north side of the Montrose Basin to near Johnshaven. It is clear, 

 therefore, that this deposit was originally a continuous and almost 

 perfectly horizontal sheet. On the Survey map dips may be seen 

 marked in this deposit up to as much as 15°, but these are quite 

 erratic, and are doubtless due entirely or almost entirely to current- 

 bedding ; there is no sign of any such irregular folding in the older 

 series of rocks. 



The identification of these outliers as belonging to the Upper Old 

 Red depends on their lithological character and general tectonic 

 relations, no fossils having been found in them. 



Tectonic Relations. 



These rocks are clearly younger than the folding which has affected 

 the subjacent Lower Old Red, and also later than a good deal of the 

 denudation which followed it. Before the horizontal strata of 

 Montrose and Boddin Point were laid down there must have been not 

 less than 8,000 feet of rock worn from the top of the Lower Old Red 

 anticline. This must, no doubt, be held to imply a great break between 

 those two sets of rocks. 



Precisely the same relation, however, holds between the Upper Old 

 Red of the Carse of Gowrie and the rocks below. That mass also 

 lies directly over the Lower Old Red anticlinal axis, and can therefore 

 only have been deposited after a similar amount of denudation. The 

 type-specimen of Holoptychius nohiUssimus was obtained from those 

 beds, so that their age admits no question. 



It will be desirable to illustrate this unconformity more fully 

 when the lithological character of these coast deposits has been 

 described, and its bearing on their age considered. Meanwhile it is 

 clear that their tectonic relations are exactly similar to those of the 

 most undoubted Upper Old Red. 



Lithological Charactees. 



Two distinct types of sedimentation occur in these rocks — the sandy 

 type and cornstone type. The former alone is developed in the mass 

 near Arbroath, where it reaches a thickness of about 200 feet. The 

 materials of this deposit are precisely similar to those of the Lower 

 Old Red on which it lies, and from which it has no doubt been 

 derived. Fairly soft red sandstone, with numerous bands of con- 

 glomerate, which are usually thin and irregular, occasionally thicker 



