82 Geological Society : — 



2. " On the discovery, by Mr. Robert Slimon, of Uppermost Silu- 

 rian rocks and fossils near Lesmahago in the South of Scotland, with 

 observations on the relations of those strata to the overlying Palseo- 

 zoic rocks of that part of Lanarkshire." By Sir Roderick I. Mur- 

 chison, V.P.G.S. &c. 



The principal object of the author is to direct the attention of 

 geologists to the recent discovery of the uppermost Silurian rocks of 

 Scotland, in which country their presence was unknown. This 

 important discovery was made by Mr. Robert Slimon of Lesmahago, 

 who in the western part of that extensive parish of Lanarkshire 

 detected very remarkable and large fossil crustaceans, the exhibi- 

 tion of which at the Glasgow meeting of the British Association 

 induced Sir R. Murchison to visit the tract in question, accompanied 

 by Professor Ramsay. 



The descending order of the strata is well seen on the banks of 

 the Nethaw river, Logan water, and other small streams ; all tributaries 

 of the Clyde. There the lower carboniferous rocks, composed of 

 several bands of Productus and Encrinite limestone, frequent seams 

 of coal and layers of ironstone, including the celebrated "black band," 

 are underlaid by the Old Red Sandstone, as largely exposed between 

 Lanark and Lesmahago. Towards its lower part the Old Red is 

 marked by a powerful band of pebbly conglomerate ; whilst its base 

 is made up of alternating red and light greenish-gray flagstones and 

 schists. 



The latter are succeeded by dark gray, slightly micaceous, flag-like 

 schists, charged with large crustaceans and other fossils, which 

 organic remains, combined with the apparently conformable infra- 

 position of the beds to the lowest Old Red, have led the author un- 

 hesitatingly to consider the Lanarkshire strata to be the equivalents 

 of the uppermost Ludlow rock or the Tilestones of England. 



These dark gray fossiliferous layers are underlaid by, and pass 

 down into, athick accumulation ofsimilarmudstones, which becoming 

 in some parts slightly calcareous, in others arenaceous, rise up into 

 a district of round-backed moorland hills, ranging in height from 

 1600 to 2000 feet above the sea ; the whole tract having been much 

 penetrated by porphyries and other igneous rocks. 



The uppermost Silurian rock of Lanarkshire contains a species of 

 Fteryyotus not to be distinguished from the species of that crusta- 

 cean so abundantly found in the upper Ludlow rock of Shropshire 

 and Herefordshire ; like which the Scotch stratum holds the Lingula 

 cornea and Trochvs helicites} (Sil. Syst). The Lesmahago deposit 

 is further characterized by the crustaceans of the group of Euryp- 

 teridse (Burmeister), which are described by Mr. Salter under the 

 name of Himantopterus . They are accompanied by another crus- 

 tacean, the Ceratiocaris . 



In conclusion. Sir Roderick pointed out the remarkable persistency 

 of this zone of large crustaceans in various parts of the world ; one 

 of the Lanarkshire individuals has a length of about 3 feet ! In 

 Westmoreland (Kendal) the Enrypterus is found in the Tilestones, 

 with many upper Ludlow fossils ; in Podolia the stratum containing 



