INTRODUCTION. 33 
such as a Delesseria alata. Beautiful as this was, it was 
equalled, if not surpassed, by specimens given me by a 
friend who gathered them at Tintock, a well-known hill in 
Lanarkshire. The stone was fine reddish felspar, and on 
this delicate ground the dark crystallizations arose some 
inches in height, much resembling a miniature grove of 
elegant pine-trees. And these specimens, worthy of a place 
in any cabinet, could be gathered in abundance, being 
broken down for road-metal, soon to be trodden by the foot 
of man and horse, or to be triturated by the crushing 
wheels of aristocratic carriages or of heavy ignoble wains. 
It is rather curious that a few hours after I had written 
the description of these beautiful crystallzations, I inci- 
dentally got some insight into the way in which they are 
formed in the great laboratory of Nature. The process, in 
all likelihood, is known to many; but as it was a pleasant 
little discovery to me, I shall mention it for the instruction 
and amusement of some of my young friends—who may be 
as ignorant of the matter as | was myself. Having some 
iodine in a hermetically sealed phial, I had occasionally 
amused myself and others by heating the phial at the fire, 
or at a candle or gas flame, and seeing it immediately filled 
with most beautiful violet-coloured vapour. Wishing to 
D 
