320 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 18 



sandstones which cap the Cairn Table ridge also occur along the hill- 

 tops to the eastward, and hence they would range by Kinnickfoot 

 into the Douglas coal-field. 



It appears, therefore, that the Old Eed Sandstone and Silurian 

 hills to the south are flanked by a thick series of Lower Carboniferous 

 sandstones, but that a short way northward, as we advance in the 

 direction of the great coal-fields, this series thins rapidly away to 

 about 50 or 60 feet in some places. Even at their greatest thickness, 

 however, these sandstones but poorly represent the enormous depth 

 of Lower Carboniferous and Upper Old Eed sandstones in the Lothians 

 and Berwickshire. 



The lithological aspect of the base of the Carboniferous group in 

 the Lesmahago district varies considerably in different localities. 

 Along the southern line, where the thick Lower Sandstone series 

 occurs, the basement-beds are reddish and conglomeratic. In the 

 Monkshead Glen they are very red, marly, and sandy, with fronds of 

 a Splienopteris. At Glenbuck they consist of hard, reddish-grey, false- 

 bedded sandstones. Below Kerse on the Nethan, the lowest bed I 

 have already described as a conglomerate formed partly out of pale 

 Old Eed Sandstone, and partly out of a whitish porphyry-dyke on 

 which the conglomerate at the point of section rests. In short, 

 towards their base the Carboniferous rocks assimilate in general 

 aspect to the Old Eed Sandstones below. This resemblance is suffi- 

 ciently close to lead one at a first glance into the belief that there is 

 a gradual passage of the one series into the other. But the peculiar 

 purplish-grey or chocolate colour and the fissile flaggy structure of 

 the Old Eed sandstones never, so far as I have seen, shade into the 

 brick-red hue and false-bedded character of the Carboniferous rocks. 



Finally, from what has been stated above, and from the accom- 

 panying Map, it will be seen that the base of the Carboniferous series 

 rests successively upon many different horizons, alike of the Silurians 

 and the Lower Old Eed Sandstones. Such a transgressive line shows 

 very clearly the unconformable relation of the Carboniferous beds to 

 the older strata on which they lie. 



Pentland and Lammermuir Hills. — Having ascertained that be- 

 tween the Carboniferous Limestone series and the Lower Old Eed 

 Sandstone there existed in Lanarkshire and Ayrshire a decided un- 

 conformity, I knew from previous examination that the same physical 

 break must occur between the Upper and the Lower Old Eed Sand- 

 stones. With the experience of the Lesmahago sections, I again 

 visited the Pentland Hills, in company with Professor Eamsay, and 

 found that the localities mutually explained each other. 



In the memoir to accompany sheet No. 32 of the Geological Survey 

 of Scotland, I have described in detail the structure of the Pentland 

 Hills. It is only needful to mention here that the richly fossiliferous 

 shales of the Upper Ludlow rock of that locality are overlaid by 

 conformable red shales, sandstones, and conglomerate-bands which, 

 there seems no reason to doubt, correspond to the similar series of 



