The Lammermuirs have an extent of nearly one hundred and fifty miles in length, by an average breadth of twenty-five to thirty miles. The axis of the chain runs from E.N.E. to W.S.W., broken at intervals by rivers and their divergent valleys, and constituting the great frontier barrier of Scotland. The Lowthers, Corston-cone, Queensberry, and the high grounds along the upper right bank of the Nith, form outliers or extensions of the general mass. Long regarded as furnishing a true type of _Graywacke_ rock, the Lammermuirs are now, by general consent, admitted into the family of SILURIANS, bearing affinities both to the Upper and Lower series, and partaking likewise in some of the characteristics of the Cambrian group. The eastern division of the chain consists of very thick beds of a coarse brecciated rock, covered on the southern side by a fine-grained clay slate. In Kirkcudbrightshire, the slate-band and conglomerate, seen on the main land, and at White Bay, in Little Ross Island, are very closely allied in their mineralogical characters. And in the center division, about Innerleithen, the intrusive traps constitute a marked and interesting feature, more particularly as they there assume a subcrystalline granite structure, and convert the sedimentary deposits into hard flinty slates, or Lydian stone. The organic remains are not abundant: they are scattered, too, at wide intervals, but still sufficiently characteristic of the formation. They consist of graptolites, encrinites, trilobites, and several genera of shells. The list of conchiferæ, in some beds, is almost entirely Lower Silurian, while the _smooth Asaphi_ would seem to connect this range of hills with the lower Silurian rocks of Tyrone and Fermanagh, in Ireland, which have furnished the only other specimens yet detected in Britain. The fossil localities are the lime quarries of Wrae, near Broughton, Greiston slate quarry, near Traquair, St. Mary’s Isle, Kirkcudbright, Loch Ryan, and Little Ross Island; and in certain graywacke beds in Liddesdale, Mr. Nicol records the discovery of “fragments of plants, not unlike the broken reeds, and other imperfect vegetable remains, seen on some carboniferous sandstones.” The collection of Lord Selkirk, from the vicinity of his residence, consists according to Mr. Salter, of—_Terebratula semisulcata_, _Leptæna sarcinulata_, _Atrypa reticularis_, _Bellerophon trilobatus_, _Natica_, _Turritellæ_, _Murchisonia_, _Avicula lineata_, _Orthonaia cingulata_, _Phacops caudatus_, _Beyrichia tuberculata_, and _Graptolites ludensis_. These characteristic Upper Silurian fossils are accompanied by a _Leptæna sericea_, and _Orthoceras tenuicinctum_ of Portlock, and appear to be of the date of Wenlock shale. Their latest historian, indeed, ascribes a vast indefinite antiquity to the whole range, and considers that the depository matter has been _twice_ reduced to a muddy arenaceous state: that a chain of hills existed in these parts at an age long anterior