THE STUDY OF ROCK-SECTIONS. 
Petrology for Students | by | ALFreD Harker, M.A., F.G.S., | Fellow of 
St. John’s College, and | Demonstrator in Geology (Petrology) in | the 
University of Cambridge. | Cambridge : | at the University Press. | 1895. 
Mr. HARKER’s contribution to the Cambridge Natural Science 
Manuals is a compact book of over three hundred pages, full of 
interesting matter, and illustrated by seventy-five drawings of rock- 
sections. With this book at his side the English petrologist (for 
this book is written for British students, and the examples are drawn 
from his own country) will find the study of rock-sections as charming 
as microscopical biology. The author insists that the identification 
of the component minerals is only part of the examination oO 
a rock-section. Its history should be read by the study of the 
mutual relations of its mineral constituents, their structural 
peculiarities, the order of consolidation, intergrowths, interpositions, 
decomposition-products, pseudomorphs, fluxion-phenomena, vesicles, 
strains, etc. s we have spent several years in Cornwall, and have 
visited many times the battle ground of British petrologists at the 
Lizard, and have had the successful teaching of mineralogical 
students in this foremost metal-mining county, where opportunities 
of studying mineralogical phenomena were ever being afforded us in 
the field, the mine, through the microscope, and in the lecture room, 
we feel, from our knowledge of the need of such a book, justified in 
recommending this work. The arrangement of the matter is good, 
with an introduction of twenty-one pages, far too short, so pleasantly, 
perhaps a little too concisely for the student, is it written. We feel, 
however, that Professor Harker would have been well advised had 
he treated of several optical subjects in his introduction which he 
has omitted because he felt that they had been well done, and more 
fully, elsewhere than he had space to devote to them. 
n a book like this, replete with rock lore, a text-book and 
a dictionary of petrology, one cannot in a brief review do one’s duty 
to it. The sections of this work are six in number, and thelr 
headings and subjects may suggest the width and scope of the 
work: Introduction, dealing with the optical properties of minerals ; 
Plutonic Rocks—granites, gabbros, peridotites, etc. ; Intrusive Rocks 
—diabases, lamprophyres, ete. ; Volcanic Rocks—rhyolites, trachytes, 
basalts, etc. ; Sedimentary Rocks—argillaceous, calcareous, ete. ; 4” : 
Thermal and Dynamic Metamorphism. 
HENRY CROWTHER, F.R.M.S. 
The Museum, Leeds, Aug. 24th, 1897. 
ee ae 
Naturalist, 
