316 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Jan. 18, 



gradually disappear, and the Old Red Sandstone then begins to form 

 an ascending series towards the Clyde, the prevailing dip being 

 E. by N. 



Carboniferous. — I have referred to the tongue of Carboniferous 

 strata which diverges from the great Lanarkshire coal-field, and 

 extends up the valley of the Nethan to within a mile of Lesma- 

 hago. The Douglas coal-field stretches north to nearly the same 

 distance from the town, and then bends south-westward between the 

 channel of the JSTethan and the base of the Haughshaw Hills. It 

 becomes greatly attenuated in the Upper Monkshead Valley, and 

 appears indeed to thin off entirely for a short distance. But a faidt, 

 which crosses the glen opposite the farm-house, throws the lime- 

 stones and coals in again along the west flank of Hareshaw Hill, 

 where the black-band ironstone was once extensively mined. From 

 this point the Carboniferous rocks expand into the Valley of the 

 Ayre, and up to the summit of the hills by which that valley is 

 bounded on the south. Here and in the Douglas coal-field, although 

 the surface often shows little else than a wide expanse of barren 

 moorland, it nevertheless conceals mineral deposits of great value ; 

 and hence districts which a few years ago coidd boast only a few 

 widely scattered hamlets, are now becoming dotted with chimneys 

 and traversed by railroads. 



A careful working-out of the details of the Carboniferous system 

 as developed in the Lesmahago district would doubtless amply 

 reward the labour. Especially full of interest are the alternations 

 of marine and terrestrial strata, the disappearance of certain beds 

 over particular areas, and the thickening and thinning of coals and 

 limestones, as well as shales and sandstones in particular directions. 

 Some of these appearances obtain, I believe, their true explanation 

 in the unconformable relation of the Carboniferous to the underlying 

 Red Sandstones to which I shall immediately advert. My observa- 

 tions among the Carboniferous strata were almost wholly confined to 

 the lower limestones and the beds below them- — in short, to the base 

 of the Carboniferous series where it rests on the Old Red. The 

 features of the junction-line I shall now proceed to describe. 



In no part of the district can the junction of the Carboniferous 

 and Lower Old Red Sandstone be more clearly made out, than along 

 the southern margin of the Auchenheath coal-field, about a mile 

 north of Lesmahago. By descending the streamlet called Kerse 

 Gill, which skirts the south side of some lime-quarries and falls into 

 the Nethan below Kerse House, we obtain a good section of both 

 formations. Near the bridge south of Kapeshall, Old Red Sand- 

 stones are seen dipping 45° E. of N. at 25°-30°. The same series can 

 be traced down the channel of the stream for fully half a mile, the 

 general dip being E. by JST. At the bridge above the lime-quarries, 

 the sandstones are mottled, purple, and white, flaggy and micaceous, 

 traversed by two small felstone-dykes. Below this bridge, the sand- 

 stones continue with the same dip, but are much whiter — so white, 

 indeed, that at first, I doubted whether they were not Carboniferous. 

 It was not long, however, before I satisfied myself that they really 



