I860.] GKIIUE OLD RED SANDSTOXK. 319 



ferous limestone is quarried at Auchtool dipping S. by E., that is, 

 almost at right angles to, and along the denuded edges of, the Old 

 Red Sandstone bank to the north. 



Sufficient evidonce has probably now been adduced to prove that, 

 in Lanarkshire and Ayrshire, strata belonging to the Carboniferous 

 Limestone series rest unconformably upon certain sandstones and 

 shales of Lower Old lied and Silurian age. Some of the features of 

 this unconformity must be briefly noticed. 



One of the first facts which struck me when I began the examina- 

 tion of this district was the entire absence of the vast mass of strata 

 below the Carboniferous Limestone, known in the Lothians as the 

 Lower Carboniferous group and the Upper Old Red Sandstone. I 

 had traced these strata from Mid-Lothian down into Lanarkshire, 

 not more than 15 miles distant from the district under review, and 

 I therefore looked to meet with them below the Carboniferous Lime- 

 stone of Lcsmahago ; but they do not exist there. 



Another feature which soon presented itself was the fact that, 

 taking as a line of measurement a certain bed of marine limestone 

 the outcrop of which is tolerably well known, the thickness of beds 

 between the limestone and the underlying red sandstones varied 

 considerably throughout the district. Thus at Auchtygemcl, the 

 section on the Nethan shows a depth of Carboniferous strata below 

 the limestone of perhaps less than 100 feet; while along the margin 

 of the Auchenheath basin generally, the thickness appears to be 

 always below 200 feet. At the bend of the Nethan below Grateside, 

 these strata are (I quote from memory) somewhere about 50 or 60 

 feet. At Hallhill, on the west side of Black Hill, the limestone 

 comes to rest directly on the Old Rod and its associated porphyry ; 

 and the same seems to be the case at Auchmcden. From this latter 

 locality, however, as we trace the limestones to the south-east, there 

 gradually intervenes between it and the Old Red an increasing 

 thickness of white and reddish sandstones. These arc well exposed 

 in a series of quarries on the top of a wooded eminence called Stone 

 Hill, in Carmiehael Parish. From where the Old Red senes is 

 covered by the Carboniferous sandstones south of Drumaben, to where 

 the limestone crops to the wCsl of Stone Kill, is rather more than a 

 mile; the angle of dip at the quarries varies from L'u to 25°, while 

 at Drumaben it is only > s : but taking it at an average of |."> . the 



thickness of Btrata between the limestone and the Devonians will 

 probably be more than L000 feet. I had not an opportunity of 

 ascertaining how far these beds extend southward--. 



The other side of the Douglas coal-field, skirting the south-east 

 thud; of t lie ELaughshaw Eills, is bounded by a marked NT.E. andS.W. 

 fault, whereby both the CSarboni&rous and old lied series are tilted 

 on end. Though 1 did not ascmd the Oarmaooup and Einnick Waters, 



I had little doubt that this fault was thinning away to S.W.,and 



that tin' same series oi sandstones which occurs at Stone Hill would 



be Pound at the head of these streams Btretohing westward into 



Ayrshire. When on the top of Cairn Table, it seemed to me highly 

 probable, from the contour of the bills, that the grey Carboniferous 



vol.. xvi. — i'\i:i i. 2 A 



