I860.] GEIKIE OLD RED SANDSTONE. '.V2 I 



beds which at Lesmahago form the base of the Lower Old Sand- 

 stone. These Silurian and Old lied shales are covered unconform- 

 ably by a thick group of sandstones and conglomerates fo rmin g the 

 Upper Old Red Sandstone, and the Lower Carboniferous or " Cal- 

 ciferous Sandstone*" series of the Lothians. (Fig. 3.) Here, then, 

 we find part of the great series of strata which is wanting at Lesma- 

 hago. "VVe see too that, just as at Lesmahago, there is a strict 

 stratigraphical succession through the Upper Silurian and the Lower 

 Old Red Sandstone of that district ; so at the Pentlands there is an 

 equally perfect sequence through the Carboniferous and Upper Old 

 Red Sandstone. The line of physical break occurs, therefore, in the 

 Old Red Sandstone. The upper part of that formation graduates 

 upward into the Carboniferous series ; the middle and lower portions 

 pass down into the upper Silurian ; and between these two gradua- 

 ting series there is in the Pentland Hills, as in Ireland, a well- 

 marked and even violent unconformity. 



As the southern districts of Scotland become more thoroughly ex- 

 plored, more especially to the south-west, the area of Lower Old Red 

 Sandstone and Upper Silurian strata will probably be greatly enlarged ; 

 and I have little doubt that the same unconformable relation will 

 everywhere be found to characterize the junction of the Carboniferous 

 and Upper Old Red Sandstones with the older rocks. 



There is, however, one other area of Upper Old Red Sandstone 

 south of the Forth to which I would advert, — that of East-Lothian 

 and Berwickshire. The flanks of the Lammermuirs arc encircled by 

 a more or less continuous zone of red sandstone and conglomerate, 

 resting un conform ably on inclined Lower Silurian shales and grits. 

 These strata pass insensibly upwards into the Carboniferous series ; as, 

 for instance, along the coast at; Cockburnspath, and in the neighbour- 

 hood of Dunse. Below the passage-beds, the thickness of this Old 

 Red series is sometimes very considerable. Thus, along the eastern 

 end of the hills, the great conglomerate south of Dunbar must be at 

 least 1500 or 2000 feet thick ; and, though the greater part of this 

 conglomerate is representative of the sandstones and marls of other 

 parts, there is still a considerable depth of sandstones between its 

 top and the passage-beds into the Carboniferous series. 



In the red sandstones of this district, fossils have been found in 

 several localities. 



The late Dr. Fleming informed me that he had found scales of 

 Holoptychius in the red sandstones <>f Biocar Point, that is, nol fa* 

 from the base of the Carboniferous -cries. Similar scales and teeth 

 were found many years ago by Mr. Stevenson in the equivalent 

 sandstones in the neighbourhood of Dunse t. I have myself found 

 them in considerable abundance along with much-mutilateil remains 



of plants ; and M r. Stevenson informs me that a very perfect specimen 

 of Cyclopteris was found in the same neighbourhood Borne year-- ago. 



* CahifirouJi Sandttonet, the name given by Mr. Bf e Laren to the . 

 Btone Bariaa bekra the < larboniferotu laxnetbsxae of the Lothians. 



+ It seems \n-\ certain, however, that then remains are not those of II 

 rjiiiis. Thai itronglj resemble some which hare been assigned to AM 



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