110 Jlie American Geologist. August. i89i 
Fig. 3. Shows diversity of form of the metallic spherules and 
disposition of these to form trains — Magnified 25 diameters. 
Fig. 4. Exhibits form and structure of the siliceous nuclei (the 
largest of these having been selected) — Magnified 25 diameters. 
EDITORIAL COMMENT. 
The Crkxitic IIvrHOTHESis. 
It must be highly gratifying to the author of this work* that 
after so short an interval as four 3'ears, he is called to issue a 
second edition, for it deals with some of the most advanced prob- 
lems of chemical and speculative geology, and is in demand only 
b}' those working geologists whose labor is in the Archean rocks. 
The most important part of this volume is that which treats of 
the origin and genetic history- of the crystalline rocks, occupying 
chapters V and YI. From his long-continued chemical and mine- 
ralogical studies in the geognos}' of the crj'stalline rocks Dr. Hunt 
derived the " Crenitic h3-pothesis " of their origin. He shows that 
none of the hypotheses that had been proposed f ull}- satisfied the 
conditions of the problem of their origin. 
There are six theories which he rejects. (1.) That which he 
stN'les endoplutonic and which supposes the cr3-stalline rocks to 
have been formed from the mass of the primeval globe as it con- 
gealed from igneous fusion, he shows, as remarked by Xaumann, re- 
quires a progressive consolidation from the sui'face downward. 
This order is the reverse of that which has been established for the 
normal succession in the growth of the crj'stalline rocks. In many 
parts of the world observers concur in the statement that these 
rocks are newer in ascending order, and gradually assume, through 
the so-called transition strata, the physical characters of the un- 
crystalline and sedimentarj- rocks. 
(2.) The exoplutonic theor}' conceives the crystalline strati- 
form rocks to have l)een formed from volcanic ejectamenta from 
beneath the superficial crust of the earth. This includes, besides 
lavas and pyroclastic rocks, the ordinar}' products of volcanoes, 
according to some of its adherents, also hydrated serpentinic and 
*Miuer(il Physiolfxiy and Plu/siofirdphy ; a second seriCH i>f Oicniical 
and Q&jhxjical Ensays, T. Sterky Hunt. Second Edition, with new 
preface. Octavo, 710 pp., Scientific Publishing Company, New York, 1891. 
