OF THE EILDON HILLS, IN ROXBURGHSHIRE. 215 
ably very near the mass of Bowden trap. The purple and yellow trap-dyke may 
probably be identified also with one (No. 29) cutting the new red sandstone in 
the “ Duke’s Glen,’ behind the Quarry Hill at Melrose, already referred to. 
I shall conclude with some observations on the structure of the Eildon Hills 
themselves. We have seen that the greywacke formation rises to within 200 feet 
or thereabouts of the level of the col or neck which unites the two principal emi- 
‘nences. At this very level occurs a tolerably marked shelf of diluvium, which has 
strongly the appearance of having been caused by a temporary sojourn of stag- 
nant water at that height. Mr Mitne has very correctly remarked, that the drift 
on the Eildon Hills includes fragments of bright red sandstone. This phenome- 
non is better marked, however, on the south side of the col or neck above referred 
to. It is an inquiry of some interest whence these fragments could possibly have 
been derived so as to have been transported by water or otherwise to so high a 
level. The last visible greywacke strata (at 5 or 6) are not much altered (whilst 
nearer the farm of Dingleton the alteration is very marked, the strata being iron- 
shot and hardened, and the direction of strike in some places changed). Here the 
rock is sandy and of natural hardness, the strata nearly vertical, and running 
almost due east and west; in short, in almost exact parallelism to the general 
stratification of the country. Yet this must be very close to the contact with 
the great mass of porphyry of the Eildons, though the junction can no where be 
perceived. In ascending slopingly to the top of the highest Eildon by its north- 
west acclivity, I found many blocks, apparently of altered greywacke, having a 
singular character, some quite injected (as it appeared to me) with felspar, yet 
_ distinguishable almost by the touch from felspar rock, having a peculiar gritty 
_ feel. These blocks appeared to have fallen from small cliffs above, which, having 
ascended, I found to display a progressive alteration or metamorphosis from the 
trap rock of the hill into a rock having in one place almost the character of 
gneiss, and which I take to be a portion of indurated greywacke caught up by the 
_ trap, and forming the greater part of the summit of the Eildon, whose bold form 
arises in part from the excessive resistance of such metamorphic rocks to the 
action of the weather. The real trap which has effected this metamorphosis is a 
_porphyritic claystone, and the whole somewhat resembles the well-known features 
_ of the geology of the Pentland Hills at Habbie’s How.* 
Repeated visits and a careful selection of specimens confirmed this view. 
Specimens of the brick-red felspar passing into claystone porphyry are found in 
4 Nos. 7, 11, 15. As we approach the top it becomes slaty, and the direction of 
_ cleavage shifts round, dipping towards the centre of the cone, the summit being 
what appeared to me the altered rock. The slaty felspar acquires green dots 
(Nos. 8 and 9.) Then we have the slaty rock shot with red felspar (12), before 
——_s,: 

























* Mr Minne describes the top of Hildon as composed of a very hard clinkstone with a grey 
i _ basis, which strikes fire with steel. But true clinkstone could not do so, being a pure felspar. 
_ VOL. XX. PART II. 3M 
