120 The Americafi Geologist. August, i899 
surface temperatures; during the present it is no longer an 
appreciable factor; there lies between the two, the period dur- 
ing which the one source of heat lost its controlling influence 
and the other source established itself in absolute control. 
This "transition epoch" was too important a one not to have 
recorded itself in marked terms. This was the transition 
epoch of the earth's history, the only transition epoch of geo- 
logical time. 
{To be continued.) 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Minerals in t'ock sections : the practical methods of identifying min- 
erals in rock section with the microscope : especially arranged for 
students in technical afid scientific schools. Dy L. M. Luquer, pp. iv, 
III, New York: D. Van Nostrand Co. 1898. 
While we welcome every English work on this subject, whether of 
British or American source, this volume deserves special commenda- 
tion. It is almost the first of those that have come to our knowledge, 
that, while designed for the student beginner, yet gets down to the 
beginner's level, omitting abstruse and mathematical discussions, but, 
with good definitions, making clear the means and the methods of 
microscopical petrography with a systematic order. Probably the most 
used English work available, hitherto, is Iddings Rosenbusch, which, 
coming from the German, possesses some of the prolixity, and the 
vague complicated expressions peculiar to the German language, and 
is besides unfit for a beginner unless he has ready at hand a willing 
and obliging instructor. The work of Harker is like the play of 
Hamlet with Hamlet left out, since it leaves out all reference to the 
use of convergent light. The book of Hatch presumes a knowledge 
of the petrographical microscope and its appliances; that of Rutley, 
which was one of the first to appear in English, is marred by typo- 
graphical and other errors, and is badly arranged. The work of Dana 
(E. S.) 1898, has an excellent chapter on the optical characters of 
crystals, "characters depending upon light," but that is only a chapter 
in a general treatise on mineralogy, while the late edition of the work 
of Brush and Penfield specifically omits all reference to optical meth- 
ods of determination. We do not mention here the great work of 
Teall (1888) because that treats specifically of rocks as masses and is 
on another plane of petrological study. Kemp's Handbook of Rocks 
has nothing on microscopical methods, and the late work of Moses 
