1909-10.] Tuesite — A Scotch Variety of Halloysite. 
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XIX. — Tuesite — A Scotch Variety of Halloysite. By J. W. Gregory, 
F.R.S., D.Sc., Professor of Geology in the University of Glasgow. 
(MS. received February 24, 1909. Read March 15, 1909.) 
The absence of china clay from Scotland has been used as a weighty 
argument in favour of the pneumatolytic or deep-seated origin of the great 
china clay masses of Cornwall and Devonshire, of southern Sweden, and of 
some of those in Germany. Kaolin, which is often regarded — I think 
correctly — as a synonym of china clay, and kaolinite, have, however, been 
occasionally recorded as occurring in Scotland. A reported occurrence at 
Troon may be easily dismissed. Thus it is only recorded doubtfully, with 
the remark that its composition has not been determined, by J. Sommerville 
and G. R. Thompson,* while John Smith -j- describes it as a bed of fine- 
grained volcanic dust deposited in water. Kaolinite has been recorded by 
Heddle j from several Scottish localities ; thus it is found in minute crystals 
in Shetland, and in a vein at the head of Glen Capel at Abington, Lanark- 
shire. 
The existence of kaolinite in small quantities and in veins is of no 
special significance, but the statement that it occurs as a bed in the New 
Red Sandstone on the banks of the Tweed appeared, in the absence of any 
local kaolinite mass or veins, inconsistent with the pneumatolytic theory. 
Hence I thought this record worthy of investigation. The material is 
known as “ Tuesite,” and was named and described by Thomson. § Thomson 
describes Tuesite as a milky-white, opaque, sectile mineral, with a composi- 
tion which is shown by two analyses by R. D. Thomson and Richardson to 
be very similar to that of kaolinite. 
There are many subsequent references to Tuesite, but none of them that 
I have seen add any correct information to that given by Thomson, and 
they afford an instance of the danger of unchecked quotation and the 
addition of probable, but inaccurate, inferences. The material is described 
by Thomson as occurring in “New Red Sandstone” on the banks of the 
Tweed. The identification of the sandstone as part of the New Red Sand- 
* Natural History of Glasgow and West of Scotland, Brit. Assoc. Handbook, 1901, p. 552. 
t J. Smith, “The ‘ China Clay’ Mine and the Water of Ayr Hornstone Bed at Troon, 
Ayrshire,” Trans. Geol. Soc. Glasgow, vol. xi., 1900, p. 238. 
X M. F. Heddle, Mineralogy of Scotland, vol. ii., 1901, p. 148. 
§ T. Thomson, Outlines of Mineralogy, 1836, vol. i. p. 244. 
