1855.] MURCHISON LESMAHAGO SILURIANS* 15 



2. On the Discovery, hy Mr. Robert Slimon, of Fossils in 

 the Uppermost Silurian Rocks near Lesmahago in Scot- 

 land, with Observations on the relations of the Paleozoic 

 Strata in that part of Lanarkshire. By Sir Roderick 

 Impey Murchison, D.C.L., F.R.S., V.P.G.S., and Director- 

 General of the Geological Survey. 



Contents. 

 Introduction. 



General Relations of the Hocks of the Lesmahago District. 

 Upper Silurian Rocks. 

 Old Red Sandstone. 

 Lower Carboniferous Rocks. 

 Igneous Rocks of the District of Lesmahago. 

 Conclusion, 

 Appendix (Sections of Coal-measures). 



Introduction. — At tlie last meeting of the British Association, Mr. 

 Robert Slimon brought to Glasgow two remarkable collections of 

 fossils from the extensive parish of Lesmahago, in which he practises 

 as a surgeon. One of these collections was derived from the bands 

 of carboniferous limestone, which there alternate with coal, and are 

 characterized by a great abundance of fine specimens of Productiy 

 Encrinites, Corals, and other remains peculiar to deposits of that age. 

 The other consisted of specimens of Crustaceans in dark-coloured 

 schist or flag, and to two or three specimens of which my attention, 

 as President of the Geological Section, was fortunately called by 

 Mr. Page. The magnificent collection of Mr. R. Slimon had, in fact, 

 remained almost unobserved, in a hall which few geologists visited. 



The moment I cast my eye over these remarkable Crustaceans, 

 which much resembled Pterygoti, and saw the matrix in which they 

 were imbedded, it occurred to me that they probably pertained to 

 the Uppermost Silurian zone. It became, therefore, necessary to 

 visit the locality in question, chiefly for the purpose of ascertaining 

 the physical relations of the dark schist with large Crustaceans to 

 the Old Red Sandstone. For, as I was aware that the genus Ptery- 

 gotus had been found as low in the Silurian rocks as the Upper 

 Caradoc band, it might prove that there was the same great hiatus 

 near Lesmahago as had up to this time been supposed to prevail all 

 over Scotland, and that no representative of the Uppermost Silurian 

 existed. On the other hand, the band in question might prove to be 

 that which I shall endeavour to show it is — ^viz. the true represent- 

 ative of the highest Silurian zone, as developed in Herefordshire, 

 Shropshire, and Westmoreland in England, in Russia on the Conti- 

 nent of Europe, and also in North America. 



Having requested Professor Ramsay to accompany me, we visited 

 Lesmahago together, and there found to our gratification, that the 

 worthy and modest Mr. Slimon had not only a much richer collec- 

 tion of the fossils in question than he brought to Glasgow, but had 

 also an accurate acquaintance with many of the prominent and de- 

 tailed features of the tract. Guided by him to the best natural sec- 

 tions, and particularly to the spot on "Logan Water," hitherto 



