Geological Account of Roxburghshire. by DAVID MILNE, Esq., F.R.S.E

( 433 ) XXXII.—Geological Account of Roxburghshire. By DAVID MILNE, Esq., F.R.S.E. ••\ [Read 5th December 1842 and 9th January 1843.] IT seems extraordinary, that no one should have undertaken a geological sur- vey of Roxburghshire, more especially as the counties to the east and west of it have been examined, and accounts of their formations were published some years ago. It cannot be from its uninteresting character, that the intervening district has been neglected; for it presents as great a variety of apparently distinct formations, as there are in the adjoining counties of Dumfries and Berwick; and some of these have long been the special subjects of speculation and controversy among geologists. The British Association, in the Report of its Meeting held at Cambridge in 1833, propounded the following questions for geological inquiry. " 1. Is the red sandstone of Kelso contemporaneous with that of Salisbury Crags; and what relation do they respectively bear to the adjacent coal-fields ? " 2. What is the exact northern boundary of the coal-field of the River Liddell f " 3. What are the relations as to age of the two series of whin-rocks, one running north-east along the Liddell in Roxburghshire, the other south-east in the neighbourhood of Melrose and Jedburgh f These questions show the opinion entertained by the Geological Section of the Association, as to the interesting geological character of Roxburghshire. But the questions which they propounded have never received an answer; a result not surprising in regard to the last of these questions, as it calls for an explanation of facts which really have no existence. A stronger proof could scarcely be adduced of the ignorance prevailing among our best geologists, of Roxburgh geology. In describing the different formations existing in this county, I shall treat of them, first, with reference to the state in which they now are; and, second, with reference to the causes which have apparently produced that state. I shall describe the formations in the following order:— I. The Stratified or aqueous rocks. II. The Unstratified or igneous rocks. III. The Diluvial or post-tertiary deposits. I shall not attempt by words, to define the geographical limits of these several formations, but content myself with referring to the accompanying map (Plate XII.), the colours on which represent the several classes of rocks I am now about to describe, and will at once shew the extent of each. VOL. XV. PART III. 6 B Plate 'XII. Royal Soc. Trans I!din GEOLOGICAL MAP of tlie COUNTY or ROXBURGH in PI Instigation of M« IIILXE'S P A P E R RocJcs in Transactions of Sandstone tbniiatwrL KOYAI, SOCIETY 11 Z formation K D1S j FelspaiJiic Trap Rack:*' ^ ,f,aL- of Jfilr.r. ' Clovs-toiies Clinics to rw? £•<" MB Juaihc Trap Rocks ^^ /Basalts Greerwtonex &cj 434 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. I.—Stratified or Aqueous Rocks. 1. The first of these which I shall describe, and which is by far the most abundant, is the Greywacke. Almost all those hills which occur in elongated ridges, are composed of this rock. It has, in most places, the usual colour of bluish grey, though occasionally the colour is red, as in the Leader near Carolside, in the Jed near Kersheugh, and in the Kale near Oxnam. Its strata vary much in thickness; some being almost as thin as paper, and others several feet in thickness;—but its ordinary character is slaty, a character for which it is indebted to the presence of mica. On this account, the greywacke rocks very generally exfoliate by the varying influence of the atmosphere, and produce a soil, wet but by no means ungenial. I am not aware that the thin strata are found anywhere in this county so hard as to produce roofing-slate; but the thicker strata afford tolerably good building ma- terials. The texture of the greywacke is, generally speaking, what is termed " fine granular." A coarser variety (amounting almost to conglomerate) sometimes occurs, as a few miles west of Galashiels, on the turnpike road, where it is quarried. The greywacke strata are in this county, as in the rest of the British islands, almost every where vertical. Any deviations from this rule observed by me, were very rare. At the Miller's Knowe, near Hawick, they dip at an angle of 80° to the south; at Kirkton, 80° to the south; at Rinkfair, about 75° to north; at Southdean Manse and at Abbotrule, they dip south at an angle of about 50°; above Jedburgh, the dip is to south at an angle of 65°; at Carolside Bridge, about 40° to the north; west of Edgerstone Rig, they make an angle of only 20° with the horizon, dipping south. In several places, the foldings or contortions of the greywacke strata are well exhibited. On Jed water, about a mile west of Edgerstone, there is a good example, in consequence of the great height of the west bank. The greywacke strata are there bent, forming a very acute angle, opening vertically downwards. The same individual strata which, at the top of the bank, form this rapid curvature, may be seen at a little distance, forming an opposite bending at the bottom of the bank. On Oxnam water, a similar fracture of the greywacke strata may be seen, and on a much larger scale; but on that account it is not so obvious, as the whole contortions cannot be easily taken into one view. Near Crailing house, they dip north at an angle of 85°., whilst near Upper Crailing mill (about two miles higher up the river), they dip south at an angle of 80°; and in the intervening parts of the river, they present extraordinary bendings and twistings. Near South Dean and MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 435 near Abbotrule, the strata may be seen dipping in opposite directions, not far from each other, affording indications of contortions on a still more gigantic scale. It is an interesting fact, as tending to indicate the direction of the forces which produced these contortions, that the greywacke strata in Roxburghshire, as elsewhere, crop out in lines which run nearly due east and west by compass. One place where I observed the greywacke strata cropping out in a different direction was in Liddesdale, above Hermitage Castle, at a place called the Grains. Its strike there is north-east by east; but this was a mere local aberration, which was the more obvious, from the strata there dipping at the small angle of 40° to the horizon. In the burn behind Melrose, which flows from the Eildons, the greywacke strata run north-west by west, and rise to these hills. This is the strike of the beds also on the Jed, \ mile from Cleslipeel, and on the Carter burn at Sykehead. It is a consequence of these gigantic foldings of the greywacke strata, in an east and west direction, that all the principal valleys in that formation run in the same direction, as is well shewn by the course of the rivers Ewes, Teviot, Ale, and Borthwick, which are the principal rivers in the district. No fossils, except some morsels of black vegetable matter, have been dis- covered in the greywacke strata of Roxburghshire. Sometimes they exhibit on their surface a curious concretionary structure, which has been by some, though I think quite erroneously, attributed to organic causes. The only metallic veins I have observed in this formation consist of hematite or red oxide of iron. They are in some places very abundant, as below Cowden- knows (on the Leader river), where they may be seen in the channel, from half an inch to an inch in thickness, filling up the natural joints of the rocks. In some places, these hematitic veins form, at their out-cropping on the surface of the greywacke strata, fantastic figures, as on the Jed at Cleslipeel. There is no doubt that this red oxide is largely distributed through the greywacke rocks. I understand that small portions of galena were formerly found in the greywacke strata, at Langholm Bridge. 2. The next class of rocks to be described is the Old Red Sandstone formation, though I am unwilling to assert, that they form a class independent of, and distinct from, the one which I am next to describe, viz., the Coal Measures. On the contrary, there are strong reasons for believing, that both these sets of rocks, though their outward and visible characters are very different, belong to the same epoch, and have only been made to assume distinct appearances by local causes, to be afterwards alluded to. At all events, there is no grand line of demarcation between them, such as, in other cases, is indicated by the interposition of beds of conglomerate, or by striking differences of dip. For the sake of distinctness, I will here treat of these two sets of rocks sepa- rately, and in the order generally followed. 436 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. The Old Red Sandstone rocks are most generally of a dull brick-red colour. In a few localities, there are strata nearly pure white, and, still more rarely, there are strata of a yellow colour. The texture of the stone is soft, and seldom compact. The picturesque character of the valley of the Jed, enclosed within steep and lofty cliffs, for many miles of its course, is mainly attributable to the facility with which that river and its tributaries cut through the old red sandstone strata.

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