482 
POPULAR SCIENCE REVIEW. 
ROCKS CLASSIFIED * 
A VERY different book from tbe foregoing is that now before us. It is 
the translation of a treatise on systematic lithology, and is a book at 
once worthy of its great author, creditable to science, and invaluable to the 
practical geologist. It is especially to be regarded as a book of reference, 
since it describes in methodical order the several varieties of rock, — igneous, 
aqueous, and organic, — which make up the crust of the earth. It is certainly 
the finest work on lithology which has as yet been presented to British 
readers, and since both author and translator co-operated in the preparation 
of this edition, we have ample guarantee for its accuracy and accordance with 
the progress of geological science. The classification of rocks adopted is 
somewhat artificial, but will, we think, be found useful. It is as follows : 
(1) Igneous , divided into basic and acidic, the basic being again sub-divided 
into volcanic and plutonic, and the acidic undergoing a similar grouping. 
(2) Metamorphic crystalline schists , including the felspar, quartz, chlorite, 
and crystalline groups. (3) Sedimentary and fragmental rocks , including the 
argillaceous, marl, limestone, gypsum, fragmental, and conglomerate groups. 
(4) Bocks of special character or bedding, comprising the serpentine, garnet , 
schorl, carbonaceous, and ironstone groups. The minerals are also systema- 
tically arranged, and their chemical, physical, and crystallographic charact ers 
are fully given. 
MANUAL OF ELECTRICITY.* 
O F the many works in Chambers’s Educational course there are but two 
or three which we consider really accurate and clearly written. One 
of them is the admirable treatise on chemistry by the late Dr. Wilson, one 
of the most excellent introductions to the science ever published. The 
present volume is intended as a sort of companion to Wilson’s book, and we 
think it is worthy in the highest degree of the place it seeks. It is well 
written, up to the most recent advance of the branch of physics on which it 
treats, and is, moreover, amply illustrated and comprehensive. The author 
is a thoroughly modern philosopher, and his book bears the impress of its 
author’s mind. Mr. Ferguson ignores the theory that electricity is what 
some of the books call a “ subtle fluid.” This view he thinks is likely to 
lead to the impression that is not warranted by experience. He looks upon 
electricity, therefore, as u a peculiar action which the molecules of matter 
'* “ Rocks Classified and Described.” By Bernard Von Cotta. An English 
edition by Philip Henry Laurence, with English, German, and French 
Synonyms. Revised by author. London : .Longmans & Co., 1866. 
t “ Electricity.” By Robert M. Ferguson, Ph. D. W. & R. Chambers, 
London and Edinburgh, 1866. 
