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XI.—Notes on the Geology of the Eildon Hills, in Roxburghshire
Published online by Cambridge University Press: 17 January 2013
Extract
The following remarks, being the result of a careful examination of a small district of country characteristic of the relations of the trap formations, are perhaps worthy of being recorded; although the general features of the county of Roxburgh have been very clearly stated in a paper by Mr Milne, published in the 15th volume of the Edinburgh Transactions.
The outburst of porphyritic trap forming the conspicuous small group of the Eildon Hills, may be stated to be surrounded by the characteristic greywacke of the south of Scotland. It forms an elongated patch on the map, extending from the west end of Bowden Muir in the direction of the town of Selkirk, and running from west-south-west to east-north-east (true) towards Bemerside Hill, on the north bank of the Tweed. The breadth is variable, probably less than is generally supposed; but it cannot be accurately ascertained, owing to the accumulated diluvium which covers the whole south-eastern slope of this elevated ridge. On this account, my observations on the contact of rocks have been almost entirely confined to the northern and western boundaries of the trap, although the other side was examined with equal care.
- Type
- Research Article
- Information
- Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 20 , Issue 2 , 1853 , pp. 211 - 217
- Copyright
- Copyright © Royal Society of Edinburgh 1853
References
page 212 note * The deviation from true east and west is less than 5°.
page 212 note † The collection of specimens referred to in this paper has been placed in the Museum of the Royal Society of Edinburgh.
page 214 note * The deposit in question occurs at the house of Holmes, exactly opposite to Dryburgh Abbey. The course of the Tweed is here north-north-west to south-south-east. The strata on both sides of the tufa mass are red and white sandstone, stratified nearly horizontally with some slate-clay. At the north junction the strata cannot be distinctly traced to within 50 or 60 yards of the trap; but, when the river is low, a better view might be had. The tufa rock, however, is modified and compacted, including large and small nodules of rounded quartz, and, in one place, includes soft angular fragments (perhaps of slate-clay), which give it almost a porphyritic appearance (specimen No. 30). The characteristic tufa rock (No. 31) may be traced 100 yards or so up a little side ravine, but is then completely lost under diluvium. The southern part of the tufaceous mass becomes very compact, and assumes the character of a very tough felspar porphyry (No. 32). The sandstone strata in contact with it are hardened and bleached in a remarkable manner.
page 215 note * Mr Milne describes the top of Eildon as composed of a very hard clinkstone with a grey basis, which strikes fire with steel. But true clinkstone could not do so, being a pure felspar.