366 Reviews—J. J. Harris Teall’s Petrography. 
we think the author leans a little too much upon dynamic metamor- 
phism, real or supposed. Thus, there is only one figure illustrating 
contact metamorphism in a sedimentary rock, and that is the some- 
what abnormal case of the chiastolite slate of Skiddaw. We should 
have gladly seen with it an example of the mica-andalusite rock 
which occurs in the same region nearer to the intrusive granite. 
But when one remembers the exceptional difficulties under which Mr. 
Yeall has accomplished his task—for the failure of the first publisher 
threatened to shipwreck the book, at a comparatively early stage of 
its issue, and the author has completed it, at hisown risk, without any 
hope of profit, and with more than a possibility of loss—it seems 
ungenerous to cavil at minor blemishes, for the book now comes 
almost as “a gift-horse.” é 
So we will allow ourselves but one other criticism. The title of 
the work does the author an injustice—it is not a Petrography, but 
a Petrology. No doubt, as he says, the work is to a large extent 
devoted to a description of the rocks so far as this is dependent on 
the examination of hand specimens; but the significance of the 
structures and of the relations of the minerals are again and again 
discussed ; indeed, the chapters on the characters and classification 
of igneous rocks, on their origin, metamorphosis, and destruction, 
are of the highest value. We lay some stress on this verbal question, 
because the confusion between the two terms Petrography and 
Petrology is so common, especially among continental writers. 
Perhaps the author would thus defend his selection of a title; but 
we have yet to learn that “following the multitude to do evil” isa 
valid excuse in science any more than in ethics. The distinction 
between a “graphy” and a “logy” is indisputable, for it rests on 
the inherent significance of words—and no concurrence of authors, 
however eminent in science, can alter this. The ‘“ petrographer” 
must be content to walk with the geographer and shake hands with 
the photographer; to receive only a bow of condecension from the 
mineralogist and the geologist. 
The dominant principle of Mr. Teall’s work we believe to be a 
thoroughly sound one. It is, that to give an accurate description of 
a rock is a vastly more important matter than to give ita name. A 
rock type is to be regarded as the ‘locus’ in which a group of 
characteristics meets, as a convenient expression of a complex idea, 
rather than as a distinct entity. Hence, though we are obliged to 
name, and are bound to define with some precision, our ideal types, 
though it is unpardonable to misapply their names—as, for instance, 
to call a rock a serpentine when it contains much silicate of alumina 
and comparatively little silicate of magnesia—still our species, as we 
may call them, should be made as inclusive as possible, and preci- 
sion should be obtained rather by addition of epithets than by 
novelty in nomenclature. 
The first chapter of the book gives an admirably clear sketch of 
the constituents of igneous rocks, describing their various forms, 
microlithic and otherwise, together with an outline of the work 
which has been done in the study of inclusions in minerals and the 
