1901-2.] J. G. Goodchild on Scottish Mineralogy. 
337 
contents of these veins at the present day may therefore be safely 
regarded as the net outcome of all these ebbings and flowings in 
the past. The mode of occurrence of much of the Chalcopyrites, 
Galena, and Blende, appears to suggest that, whatever may be the 
age of some of the others, these minerals may have been intro- 
duced in their present state in comparatively-recent geological 
times. Perhaps they are the result of that phase of volcanic 
activity which formed the closing episode of the outbreaks to which 
the vast pile of eruptive rocks of the Hebrides and Arran, etc. 
are due. There is good reason for believing that most of the 
present contents of the North of England lead veins date from 
this same period, and that they are all of later date than the last 
great movements of upheaval of the land.* There may well have 
been remnants of older deposits in the Leadhills veins, formed at 
any one of the periods of volcanic history prior to this, and 
later than the formation of the fissures in which the veins 
occur. 
The associations of the Cerussite at Leadhills are of interest, and 
throw some light upon the history of the mineral. Cerussite 
is, of course, of later origin than the Galena. It is later, also, 
than the associated Chrysocolla, because, wherever the two occur 
together, the Cerussite occurs invariably upon this mineral. It is 
later than part of the Pyromorphite, for the same reason. But 
the growth of the associated Pyromorphite must have gone on 
concurrently with that of the Cerussite, because the two minerals 
are occasionally intergrown, and Pyromorphite, in the form of 
tufts of minute crystals, is sometimes sprinkled over the finished 
Cerussite. Exactly the same relationship as that between 
Cerussite and Pyromorphite can be made out between the former 
and the Monosymmetric Hydrous Copper Carbonate, Malachite. 
Its relation with the rarer minerals, Leadhillite, Caledonite, 
Linarite, and Lanarkite, are of the same nature. But the Cerussite 
is older than much of the Calcite, and also of the Limonite. All 
this points to Cerussite as being one of the latest-formed minerals 
in the veins. Perhaps that fact may serve to explain why it is 
that no clear evidence seems yet to have been obtained of the 
* Trans. Cumb. and Westd. Association , part vii. p. 108 (1883) ; and Proc. 
Geol. Assn., vol. xi. No. 2, p. 57. 
PROC. ROY. SOC. EDIN. — YOL. XXIY. 
22 
