88 
THE GEOLOGIST. 
Erratum. — In my last article, in lieu of the note at foot of page 34, 
read, — " Most of the alum thus produced is no doubt iron-alum, i.e. it 
contains sulphate of iron, and no alumina.'' Sulphate of peroxide of 
iron and sulphate of alumina, being isomorphous salts, can replace 
one another in their combinations without causing a change in the 
crystalline form of the product. Thus, if these two salts be dissolved, 
they cannot be separated by crystallization : every crystal will contain 
both. This is often a cause of great inconvenience ; for, when 
common alum (sulphate of potash and alumina) be mixed with, or 
replaced by, iron-alum (sulphate of potash and iron), it cannot be 
employed in dyeing, calico-printing, &c. Now, this must be inevitably 
the case with the alum produced by the spontaneous combustion of 
the coal-beds of I'Aveyron, mentioned in our preceding article, from 
the decomposition of the iron-pyrites. 
REVIEWS. 
Siluria. The History of the Oldest Fossilifcrous Rocks and their Foundations ; tvitk 
a Brief Sketch of the Distribution of Gold over tlic Earth. By Sir R. I. MuR- 
CHisoN, &c. (Third Edition, including the " Sikuian System.") With Maps 
and many additional lUustrations. 1859. 8vo. London : Murray. 
Tnis long-expected book has at last appeared, and presents a result well worthy 
of the care and pains that have l)een evidently bestowed upon it ; and its handsome 
appearance prevents regret for any delay in its production. The printers, with 
good paper, clear tyjie excellently printed, and the skill they have displayed in 
making the most of the numerous woodcuts with which it is illustrated, well 
merit the passing word of praise which the reviewer is licensed to give them. 
The chief attraction of the new edition (we object to style it " the thud," for 
the greater and original work, the " Silurian System," must then be regarded as 
the first) is in its matter. Designed as the book is to give us the history of the 
most remote periods of organic life upon our planet, every new word of truth which 
the author has elicited in the foiu years since he last revised his former lal)Ours — 
from the thick and ponderous records of the wonderful rock -masses and mountainous 
regions of which the Silurian region offers the tyjics — will be looked for and sought 
out with eager eyes and anxious expectation. As we look with intense interest 
upon every trace of the first existence of our race upon this planet, and prize the 
intrinsically worthless flint or stone beyond the cost of gold, because some unknown 
human hand has chipped it into barbarous shape of arrow-head or axe, so with still 
more wonder do we regard the rain-prints, the worm-tracks, and the creeping things 
of that " long, long ago," when life first, as far as the traces of it have yet been tUs- 
tinctly ol)served, gave its great distinctive and marvellous feature to that world 
which " was our cradle and which will be our grave," — the scene of all our loves, 
and ho|5es, and fears, our joys and sorrows, — linked to us by every tie of friendship 
and affection, and dear to us even in the days of sonow and of tears. 
It is something in such an active and intelligent world to attain eminence — to 
reach that point from whence we can look back or domi — to be able to say we 
have done good service, or that we have surpassed our fellows in the intellectual 
race, — and so well estaljlished is the veteran eminence of Sir Roderick Murchison 
that we may acknowledge it without flattery or adulation ; but, like as the poorer 
portion of humanity envy the good coat on every man's back they see, so there are 
some smaller minds even in scientific circles who would attempt to detract from 
the fame which a long, active, and useful life has fairly earned ; and we are glad 
