Review of Recent Geological Literature. 181 
younger than the secondary strata of the di.strict." But in 
the absence of other evidence such reference was merely 
"begging the question." How far the appearance and structure 
of these rocks fall short of determining their age may be in- 
ferred from the remark recently made by the director-general 
of the geological survey of Great Britain that "he is unable to 
recognize any essential difierence of structure or composition 
between the Tertiary igneous rocks and those of earlier geo- 
logical age." 
During the long process of these eruptions occupying per- 
haps a great part of the Tertiary era a gradual change in their 
nature occurred. The early acid ejecta of felstone-forming 
matter slowly but steadily gave place to basic gabbro-forming 
outflows. The former were apparently viscous or quick cool- 
ing lavas and seldom spread more than ten miles from their 
focus. The latter cooling more slowly or being more liquid 
reached a distance of sometimes fifty miles before consolida- 
tion occurred. 
REVIEW OF RECENT GEOLOGICAL LITERATURE. 
Solar heat, Cravitatioti and Sun-spots. By J. H. Kedzik. Chicago, 
S. C. Griggs and Co, 1S8(). 12mo, pp 304, with supplement of Kjpp. 
Thi.s little volume is an astronomical and physical free lance which 
pierces some of the commonly accepted doctrines or notions concerning 
the solar system which do not bear the application of keen reasoning. 
Its thrusts are not by any means limited to prevalent popular notions, 
but some of the physical doctrines which have been taught by emin- 
ent astronomers, and which are found in our common text-books are 
treated with equal severity. The scope of the book is evinced in its 
title, and the three parts are treated consecutively, but the treatment 
and the subject matter so shade off from one part to another that in the 
philosophical ensemble there are no breaks. The second and third parts 
are logical portions of a discussion begun in the first part, and the 
value of the whole, no less than its interest to the reader, culminates 
in part three, in which the author oirers a simple but plausible explana- 
tion of the existence of sun-spots. 
To the geologist the topics and discussions are important, especially 
to those who inquire into conditions and causes that are not patent to 
sensible apprehension. The author possesses a fertile scientific imag- 
ination, one of the very first qualifications for scientific research and 
discovery. "In so boundless a field as the universe, where the un- 
known bears so large a proportion to the known, and the disproof of 
theorie.o, however grotesque and extravagant, is difficult, the tempta- 
