O. melding — Old Red Sandstone of Forfar sJiire. 407 



discordance might be small or non-existent between the top members 

 of the Lower and the base of the Upper. The sections here described 

 furnish a complete answer to this objection. The beds on which the 

 Upper series here rests are the Arbroath sandstones, near the top of 

 the Lower series. They are dipping at 20° - 25° to the south-east — 

 the maximum inclination shown on this side of the anticline — while 

 the irregular surface on which the Upper series rests is broadly 

 horizontal. Hence it is perfectly clear that — 



( 1 ) The folding of the Lower series was subsequent to the deposition 

 of the ivhole of that series. 



(2) The extensive denudation by which the anticline was planed 

 off flat was entirely subsequent to the deposition of the whole Lower 

 Old Red. 



(3) The deposition of the Upper Old Eed was subsequent to the 

 folding and denudation. 



There remains the question whether this folding and denudation can. 

 be referred, wholly or in part, to the period of the Orcadian Old Red. 

 The only facts which may help to a conclusion on this point are these : 

 The upper beds of the Forfarshire Lower Old Red, to which the folding 

 is certainly subsequent, probably are the equivalents of part or the 

 whole of the Orcadian series ; either that, or we must admit the 

 enormous total thickness of the Old Red, which is the difficulty so 

 often felt before. It should be noted, too, that no natural top toi the 

 Caledonian series is anywhere seen, so that there is certainly no 

 evidence that sedimentation ceased in that area any sooner than further 

 north. Again, we have the fact that the Upper Old Red of the Moray 

 Firth, some of which has been concluded, on paleeontological grounds, 

 to be older than that of Fife (Home, 1901), is itself generally 

 considered to rest unconformably on the Orcadian series. It would 

 seem, therefore, that though it is just possible that a part of the great 

 interval of time represented by this unconformity in Forfarshire may 

 be accounted for by the Orcadian deposits, a large part of it at least 

 must have been subsequent to the formation of those beds. The 

 magnitude of the unconformity in Forfarshire has been sufficiently 

 demonstrated. Its magnitude elsewhere and its general significance 

 must be discussed in a subsequent communication. 



Summary of Conclusions. 



The Lower Old Red Sandstone of Forfar and Kincardine is upwards 

 of 14,000 feet in thickness. No indication of a base or natural top is 

 seen in the district. The characteristic fossils of this series have all 

 been obtained from its middle beds within a vertical range of less 

 than 4,000 feet. There is no palaeontological evidence of the age of 

 the beds above or below that zone. It is concluded, on physical and 

 palaeontological grounds, that the fossiliferous beds of the Orcadian 

 area are really younger than those of Forfarshire, but there is no 

 proof that the higher part of the Forfarshire series was not con- 

 temporaneous with the Orcadian deposits. 



The folding of the Lower Old Red strata into the syncline and 

 anticline parallel to the Highland boundary fault took place sub- 

 sequently to the deposition of the ivhole of those strata. This folding, 



