362 Proceedings of the Royal Society of Edinburgh. [Sess. 
stone was in accordance with the view advocated a year later by Milne 
Home in his essay on the Geology of Berwickshire,* that the Red Sandstone 
of south-eastern Berwickshire and the adjacent parts of Roxburghshire was 
post-Carboniferous in age, and therefore belongs to the New Red Sandstone. 
This view was soon disproved, but Tuesite has still been assigned to the 
New Red Sandstone. One author is even more precise, as he refers it to 
the Bunter, for he says that it occurs “ im bunten Sandstein.” j- Thomson 
remarked that Tuesite “ makes excellent slate pencils.” Dana J cautiously 
remarks that it is “ used sometimes for slate pencils,” while Bristow § in 
1861 repeats the statement that it “ makes excellent slate pencils,” as if it 
were still quarried for that purpose. 
As the natural mode of occurrence of material found in any quantity in 
the New Red Sandstone would be in beds, and as Dana described it as 
occurring in seams, I therefore visited the locality, expecting to find that 
Tuesite is a kaolinite occurring in beds in the New Red Sandstone, and that 
it had been worked to some extent between 1830 and 1860 for slate pencils. 
Tuesite, however, is not kaolinite. It is not found in beds ; it does not 
occur in the New Red Sandstone, and it was apparently never worked for 
slate pencils. It is a variety of halloysite, which is found in veins in the 
Old Red Sandstone at the junction of the Upper Old Red Sandstone and 
some intrusive igneous rocks; and so far from being worked for slate 
pencils, the largest specimen of it that was ever found is reported to have been 
only the size of a man’s fist ; and though the material was collected at one 
time by children and used by them for slate pencils, it does not appear ever 
to have been actually worked for this purpose. 
The only precise information as to its locality is given by Heddle, who 
said that it is found on the right bank of the Tweed about one mile below 
Drybridge. I accordingly visited this locality, and found some cliffs con- 
taining beds of red sandstone about a mile below the Drybridge Suspension 
Bridge, but could find there no trace of anything that would correspond to 
Tuesite. Searching up the river, I found in the ground of The Holmes, a 
little to the south of a rock beside the river known as Hare Craig, half 
a mile from Drybridge, some veins of white material which, though not 
Tuesite, represented an approximation to it. Subsequently, guided by Mr 
Thomson of St Boswell’s, by the kind permission of Norman Ritchie, Esq., 
the proprietor of The Holmes, I was able to find some small fragments of 
* D. Milne [Home], “A Geological Survey of Berwickshire,” Prize Essays and Trans . 
Highland and Agricultural Soc. Scotland , new series, vol. v., 1837, pp. 206-211. 
t Hintze, Handbuch der Mineralogie, vo\. ii. , 1897, p. 840. 
+ Dana, System of Mineralogy, 6th edit., 1892, p. 685. 
§ H. W. Bristow, A Glossary of Mineralogy, p. 389. 
