JUKES S MANUAL OF GEOLOGY. 
139 
Whatever be the reality, it is unwise in an author to confess haste, 
or want of time, in the preparation of a hook; as it is not polite to the 
reader to be told that the odds and ends of the author’s time are good 
enough for him. As has been remarked by one well acquainted with 
human nature:—“ Confusion and perplexity in writing is, indeed, with¬ 
out excuse, because any one may, if he pleases, know whether he un¬ 
derstands and sees through what he is about; and it is unpardonable for 
a man to lay his thoughts before others, when he is conscious that he 
himself does not know whereabouts he is, or how the matter before him 
stands. It is coming abroad in disorder, which he ought to be dissatis¬ 
fied to find himself in at home.” 
In treating of Lithology, Mr. Jukes has committed, as we think, a 
serious error of judgment in writing the formula for silica, Si 0 2 , instead 
of Si 0 3 . Every chemist knows that it is a matter of taste which for¬ 
mula be adopted, and therefore the almost universal rule of using Ber¬ 
zelius’s formula should not be lightly departed from. It is used by all 
English and American mineralogists, with the exception of Mcol; by 
all Erench and Swedish writers; and by all the more eminent of the 
German school—Bammelsberg, Bose, and others. Under these circum¬ 
stances, Mr. Jukes was not warranted in adopting in a Student’s Manual 
a new-fashioned nomenclature, which is confessedly on its trial. In one 
respect he has adopted an important principle, in discussing the relative 
quantities of oxygen in the acid and bases of the minerals, including 
the peroxides as well as the protoxides. Mr. Jukes, however, could 
hardly have been aware that this principle is one in daily use in every 
laboratory, and that what are called mineralogical formulae (as distin¬ 
guished from chemical formulae of minerals) are founded on this well- 
known principle, and used by the whole Erench school of mineralogists; 
or he would not have attributed its discovery to his friend, Professor 
Sullivan, who, we are certain, must have been equally surprised as our¬ 
selves at the following passage in the preface:— 
“ In selecting the minerals for description, I wished to limit myself to those which 
are rock-constituents either commonly or occasionally. Dr. Sullivan also examined 
these descriptions for me, and pointed out a certain relation which might be traced in 
them, between the proportions of oxygen in the acid to that in the base, by means of 
which relation the close connexion between allied minerals is made more obvious, and 
placed on a more systematic basis than hitherto. This relation is indicated by the ex¬ 
pression, ‘ 0 in a : 0 in b,’ in the line which Dr. Sullivan has added to each of the mi¬ 
nerals. It will be, I believe, of interest and importance to the chemical mineralogist. 
By means of it the essential connexion, for instance, between Labradorite and Comptonite, 
and between Orthoclase or Albite and Stilbite, and the fact that the Zeolite is merely a 
hydrated form of the feldspar, is made remarkably prominent.” 
Mr. Jukes might with equal justice have assigned to his friend the 
invention of the Buie of Three. On the whole, the lithological part of 
the hook is well and clearly written, and will prove of great service to 
the student, who can interpret the chemical formulae with ease. In 
the classification of rocks of igneous origin, the authorities followed are 
Daubeny, Cotta, andD’Archiac. In page 62, Professor Bunsen’s attrac- 
