PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
257 
The banks of the stream which winds through the glen exhibited various 
sections of strata consisting chiefly of sandstones and impure limestones ; and 
on arriving at a steep bank of shale containing narrow bands of the latter rock, 
one of the vice-presidents called the attention of the party to the circumstance 
that these deposits rested upon Old Red Sandstone, wliich appeared in the bed 
of the stream, and were evidently the lowest members of the Carboniferous 
system in the district ; at the same time remarking the strong resemblance these 
thin-bedded strata presented to the " Ballagan beds," immediately succeeding 
the Old Red Sandstone of the Strathblane and Campsie districts, so well 
described by Mr. Young in the first number of this Society's Transactions. 
In one part of the "gill" an extensive fault was observed, crossing the stream 
at right angles, producing a vertical displacement of the strata to the extent, 
probably, of one hundred and twenty fathoms, so that there is a sudden transi- 
tion from the Old Red Sandstone to the Coal measures, witli their characteristic 
organic remains. Further down the stream a thick bed of limestone, containing 
JProdudus giganteus, indicates the base of the Carboniferous system, and a 
relative depth of nearly four hundred fathoms below the " ell coal," which 
occupies a position near the upper stage of the Lanarkshire coal-field. They 
then took the shortest route to Crossford, where the Xethan Water unites with 
the Clyde. Here they were joined by Laird Templeton, an enthusiastic local 
geologist, who led the way up the valley of the Nethan. On either side of the 
river fine sections presented themselves, and it soon became apparent that the 
rocks to be examined were chiefly of marine limestones and clay ironstones, 
with shales and sandstones, some of the deposits being evidently of estuary 
origin, and iu all likelihood equivalents of the strata in the neighbourhood of 
Lennoxto'WTi, on the north-west margin of the great coal basin. The only- 
igneous products observed were some rolled fragments of a light-coloured fei- 
stone porphyry in the bed of the stream, with a smiilar rock used as road metal, 
indicating a trap-area at no great distance. In the lower part of the Nethan 
hills the strata formed precipitous banks, at one point attaining an elevation of 
about three hundred feet above the bed of the stream — a fault causing a down- 
throw to the extent of several fathoms. Further up the river an exhausted 
opencast coal-pit was observed. Doubts were soon removed as to th& true 
position of the strata, for before long the fossils of th^ Lower Limestone series 
presented themselves in the form of various Brachiopoda, the Lingiila iron- 
stone indicating a higher stratigraphical order than the Productus limestone of 
the Braid wood gill. Under a projecting mass of strata a fire was kindled from 
coal supplied by a seam on the spot, and coftee was prepared and serv^ed out to 
the willing recipients, who had been under the necessity of making considerable 
exertion in threading their way among the numerous blocks of stone strewn on 
the banks of the stream. At the base of the lofty eminence on which 
Craignethan castle stands, a bed of shale was pointed out by Mr. Templeton as 
containing numerous fossils ; and here the party left the course of the river in 
order to visit the famous archetype of Sir Walter Scott's castle of Tillietudlein. 
A great portion of the edifice has been removed to build the neighbouring farm 
houses ; but two towers still remain, with part of a solid wall of hewn stone 
perforated with loop-holes. From the commanding position, the prospect was 
interesting in the extreme. Round the base of the cliff on which the castle 
stands winds the Nethan, fringed with leafy verdure, and away in the distance 
beyond an undulating district the eye could embrace the south-eastern limit of 
the great coal-field of Scotland. The excursionists then retraced their steps, 
and on returning to Crossford examined Laird Templeton's collection. 
VOL. IV. 
