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Salisbury Craigs June 1838 Geological Notes

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Salisbury Craigs

There can be only 4 theories proposed,

1s stream of lava: this impossible because upper junction is angulo- irregular like lower - the sandstone & shale metamorphose. (The former spotted with brown stars, which are during cavities full of loose grains semi-crystalline,— also b greenstone stained purple &

less crystalline - perhaps rather more amygdaloidal.

2d Theory cause of elevation. – this impossible because often overlying conformable strata.

3d horizontal injection & subsequent elevation.

3d theory none of hill formed at bottom of sea, of same structure as rest of hill in this neighbourhood (& as line running NE from Arthur, showing an escarpment in miniature very like Salisbury Craigs), & afterwards injected when in this position & line since modified & degradation. This had injected greenstone

 

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Salisbury Craigs run N = S

[annotated diagram] E A (B) (W??)

[diagram] this more true scale

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having aided in determining this form I believe in this theory – that the strata were inclined at angle say 20° to 30° & (that same cause continuing to act which first formed the ridge) fluid rock was injected between strata occasionally cracking through [tunnels] (as at A) for this hypothesis will explain all appearances denude hills in line (B) & the mass will appear perfectly conformable at X, at (C) P gap will have a wall in front dipping in, now this is seen in two spots at end opposite to Holyrood, between which a dike might be thought to run had another removal further on clearly showed the remnants of sandstone was mere buttresses against a form of trap. Now on same view at top of cliff we

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ought to have trap rising in front in wall though this cannot be seen very clearly from want of sections such as A at right angle to cliff, (& perhaps wall not becoming quite vertical though it is nearly so), yet at W end this structure can be nearly traced & at East end nearly in centre

[Diagram] this kind of structure may be observed the section not becoming at right angles. In note book there is drawing of section of end of Salisbury Craigs near Holyrood House where the cliff of greenstone rises quickly & then were parallel to strata now there is just what might be expected.

lastly on this view wherever the greenstone

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rises higher then conformable strata would allow it – this must be at busset edge of strata & at a point projecting outwards of general line, (but the kind of elevation of hill, render this difficult to be certain of)

On the SE (?) side or side fronting Arthur's Seat, denudation has generally removed all sandstone, excepting patches, which are extremely bad & those only on sides toward ends of Craig in position which may be compared to A — X (1)

In some part the slope appears to be greenstone.

The Basal line of dykes might be thought & as it rose (sketch) this lines

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lowest form a semicircle – cliff – form of Craigs entirely due to denudation – height partly thickness of bed which perhaps increases in centre) & partly from becoming intersections of dike & the great mass of greenstone has determined the point when denudation ceased.

[insertion:] I am sure of this at both ends: denudation would make one end greater & the other less.

The upper surface of greenstone more amygdaloidal then lower hence capping of sandstone probably there & no doubt would be lifted up, & thus thinner it got from front vertical backs, the more easily it would be lifted. But it may be said why will not front theory do – viz horizontal injection & subsequent elevation – in first place upper plain is not horizontal but extremely irregular – if so lower plain could be nearly horizontal

 

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except in one aspect, where outburst took place, but this is not true for, the matter has risen nearly vertically leaving a mere [sketches] fringe of sandstone both at Holyrood end house & at other well known end. – it does not explain form of hill bulging outwards & as I have said the upper surface is not a plain. – Moreover injection is exceedingly impossible in horizontal strata, & if there had been, there would have been small dike in upper strata which are absent.

Arthurs seat old submarine Volcano wreck. CC ring of cemented red porphyry (like sandstone) (& like Andes rocks) round centre of sand porphyritic trap

 

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The only other case I have to mention is that in front of upper part of great cliff of greenstone there were many several veins &, two or three inches thick passing into threads, parallel to great stratum of greenstone;— sometimes however oblique & connected with patches some of which rather angular & I have given careful figure of some in my note books – at (there are specimen also) compose colour red, composition amygdaloidal as well as several – little nests, threads of same substance curved, branching & were greatly thickening & therefore, clearly scored of segregation. – stretch of fluid matter pumped up – very much felspar however. Appeared almost as there had been spaced between the eyelets of felspar