Correspondence—Dr. Malcolm Maclaren. 477 
quartzite. Dr. Peach describes these as ‘‘exactly similar to those 
which characterise three of the zones into which the upper part of the 
Cambrian quartzite or ‘pipe rock’ of the North-West Highlands has 
been divided by the Geological Survey” (p. 44), and reading between 
the lines one can see how strongly he has been impressed with the 
evidence. Yet these rocks are nowhere stated, in map or memoir, to 
be Cambrian. Most unfortunately the final proof is lacking; careful 
search in the dark shales of the north of Islay has failed to yield any 
trace of the fauna of the Olenellus zone where its presence might. 
confidently have been predicted. 
The reasons for the great caution with which this subject has been 
handled are not explicitly stated in the memoir; we are left to gather 
them for ourselves. If the Islay quartzite be Cambrian this carries 
with it important results in Highland geology, as this quartzite extends 
into Jura and Scaba. By means of its boulder beds it can be identified 
with certain quartzites in Argyllshire and with the quartzite of 
Banffshire. The Cambrian colours would sweep into the mainland, 
reaching right across Scotland. The Central Highland schists would 
be a sub-Cambrian formation, not always certainly. separated by an 
unconformability from the quartzite, and much of the folding and 
metamorphism of these rocks must be of post-Cambrian date. This 
gives us pause, and we can sympathise with the authors in hesitating 
to found generalizations of this order on evidence which is not in itself 
incontrovertible. 
The memoir, for the area covered, is a brief one, not cumbered with 
topographical or petrographical details. It is illustrated with some 
fine photographic views and contains a bibliography of Islay geology. 
The editorial work has been well done, and the contributions by the 
different authors are skilfully joined, so that the chapters read 
smoothly throughout. The book gives us the impression of minutely 
careful work, carried out in a spirit of judicial impartiality and 
described with clearness and reserve. The unsettled problems of the 
geology of Islay lose none of their fascination from the treatment they 
receive in the memoir, and Islay remains one of the most beautiful 
and perplexing of the islands of Scotland. 
CORRESPONDENCE. 
SOURCE OF AUSTRALIAN ARTESIAN WATERS. 
Srr,—In your September issue your reviewer mentions incidentally 
Professor Gregory’s views on the source of Australian artesian waters. 
These views are perhaps best illustrated by the following quotations. 
‘*Most of the water is an old accumulation, some of which may have 
been derived by percolation from meteoric sources; much of it is 
probably of plutonic origin; and some of it may be old sea-water from 
the Cretaceous beds” (‘‘ Australasia,” pp. 104, 105). ‘‘It is there- 
fore possible to explain the occurrence of the deep-water supply 
in Australia independently of the present rainfall” (‘‘The Dead 
Heart of Australia,” p. 288). I have elsewhere in your columns 
(November, 1906) shown that the ‘plutonic’ origin or ‘juvenile’ 
state of geyser waters is far from being established. I now desire to. 
