322 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 18, 



There can be little doubt, therefore, that the red sandstones, marls, and 

 conglomerates of the south-east of Scotland are the representatives 

 of the " Dura Den Yellow Sandstones," and the "■ Upper Old Red " 

 of Ireland . They differ very widely in aspect from the Lower Old 

 Eed sandstones of Lesmahago ; and if these sandstones were present 

 in Lammermuirj they would be found to be covered as unconform- 

 ably by the Old Red conglomerates and sandstones of East Lothian 

 and Berwickshire, as, a few miles to the west, they are by the Old 

 Red and Carboniferous conglomerates and sandstones of the Pentland 

 Hills. 



In short, throughout the whole of central Scotland the Upper or 

 Holoptychius-beds of the Old Red Sandstone are found to graduate 

 by almost imperceptible stages into the Lower Carboniferous series. 

 The two formations form one great lithological whole ; and we can in 

 general define their mutual limits on the map only by an arbitrary 

 shaded line. But they are both strongly marked off from the great 

 series of chocolate-coloured sandstones of Lanark and Ayrshire, alike 

 in mineralogical, stratigraphical, and pakeontological aspect. That 

 series graduates downward into® the Upper Silurian, with which it 

 forms one continuous whole ; and between these two formations and 

 the two former, occurs the great physical break above described. In 

 fine, the Upper Silurian and the Lower Old Red Sandstone of south 

 Scotland form physically one connected group, the Upper Old Red 

 and Carboniferous form another, and the two groups are every where 

 separated by a marked unconformity. 



Physical Geography of South Scotland during the Old Red Sand- 

 stone and Carboniferous periods. — The _ facts presented in this paper 

 seem to afford some indication of the contour of the southern part of 

 Scotland during the accumulation of the Old Red Sandstone and 

 Carboniferous series. 



At the commencement of the Upper Old Red period, the Silurian 

 and Lower Old Red Sandstone had been considerably altered from 

 their original horizontal position. In the district of the Pentland 

 Hills the disturbance amounted even to verticality, while in Lanark 

 and Ayrshire it consisted of a series of gentle anticlinal folds, which, 

 however, seem to have been materially increased in inclination during s 

 subsequent periods. Probably more or less in connexion with this 

 disturbance are the numerous and often extensive protrusions of 

 felspathic rocks which intersect the tilted strata. Much additional 

 light requires to be thrown on these changes, as well as on others 

 which may have taken place during the interval represented by the 

 unconformity above described. At present we know little more than 

 that the disturbing movements had ceased before the commencement 

 of the Upper Old Red Sandstone. 



It was on the uneven surface left by these movements, that the 

 Old Red conglomerate and sandstones of the Lothians and Berwick- 

 shire began to be thrown down. I think there is good evidence to 

 prove that, when this period began, the gi'cat Silurian region of South 



