214 PROFESSOR FORBES ON THE GEOLOGY 
we observe on the same sandstone by another patch of trap tufa on the south 
bank of the Tweed, opposite Dryburgh Abbey, to which I was directed by Mr 
Minne’s map, and which perfectly resembles the Melrose tufa; but it is evidently 
separated from it by the entire mass of the Eildon Hills and the adjoining grey- 
wacke rocks.* 
The Melrose tufa is completely lost to the north, in consequence of the ancient 
excavations occasioned by the river Tweed as already mentioned; it sinks under 
flats and mounds of débris. But it may be traced to the eastward in the bed of the 
Huntly Burn, close to the house of that name, and to the villa of Chiefswood. It 
also extends to the Rhymer’s Glen, forming evidently a tongue, which runs up be- 
tween the narrow belt of greywacke which continues to fringe the trap of Bowden 
Muir and the well-marked greywacke ridge parallel to it on the north, which 
stretches to Faldonside. The section in the Rhymer’s Glen is not without inte- 
rest. Characteristic trap tufa (No. 26) first appears from under the detritus of 
the valley in the bed of the small stream. This unquestionably belongs to the 
same mass as the Melrose tufa. It may be traced up the stream of the Rhymer’s 
Glen, until it passes into a yellowish felspar rock in a gradual manner, which is 
probably in contact with the greywacke strata which succeed in almost vertical 
strata. Some of these strata are exceedingly hard, and form the barrier at the 
first waterfall. It is here in contact with a singular bed of a coaly‘appearance, 
which I believe has been mistaken for an indication of the coal formation, 
which, however, it cannot be, as it is interstratified with the hardened strata of 
greywacke just mentioned, which, it may be added, include traces of common 
galena (No. 24), and are traversed by calespar veins (No. 25). The dark bed is a 
shale (No. 23) resembling alum shale, mechanically diffusible in water, and in- 
cluding soft whitish fragments resembling steatite. At the highest waterfall in 
the Rhymer’s Glen, the greywacke strata (which here run in a direction of east 
by north) are interrupted by a dyke of felspathic trap, sometimes of a purplish, 
sometimes of a yellow colour, and which I have no doubt is the same vein as may 
be discovered in the greywacke on the east side of Cauldshiels Loch (No. 20), not 
far from its contact with the main mass of the porphyry of Bowden Muir, of 
which this vein may be an offset. The waterfall above mentioned is unquestion- 
* 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 com- 
pacted, 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 porphyritie 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 com- 
pact, 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. 

