Reviews—Professor J. P. Iddings—Rock Minerals. 568 
by the pitting which has resulted from their successive readjustments. 
The interspaces between the pebbles are almost free from sand, but 
lenticular seams of sand occur, which may have been protected from 
removal by wind, when the pebbles formed a continuous covering. 
There are places in our own district where it does not appear that 
concentration took place, and the sand with pebbles marking the 
situations of temporary streams still persist as originally laid down. 
The occurrence of millet-seed sands in the Trias is too well known 
to need further comment, and they have always been attributed to 
wind action. Professor Watts,' too, has shown that the surfaces of 
the Mount Sorrel granite, when freshly uncovered from the mantle of 
Trias, show very characteristic wind etching, and at Croft the under- 
lying igneous rocks have their joints widened and their vertical 
faces undercut in a way that could only be produced by wind. 
‘Dreikanter’ occur sparingly in the pebble deposits. They are not 
common even in recent deserts, for only the surface pebbles can come 
under the influence of the wind. 
This paper is not intended as a description of the Triassic rocks 
themselves, but to institute a comparison between the features and 
activities of existing deserts and the Trias rocks of our own country. 
The question has been discussed entirely from the physical standpoint. 
The paleontological aspect still remains to be considered. The animal 
and plant associations, and their adaptations to the peculiar circum- 
stances under which they live in the desert, should find their 
counterparts in the Trias, if arid conditions existed during their 
formation. 
ey ENV EE WV Sie 
I.—Rocx Minerats. By Professor JoszepH P. Ippines. (New York: 
Wiley & Sons, 1906.) 
URING the last ten years so many advances have been made in 
the microscopic study of minerals, and so many new species haye 
been recognised among the minerals of rocks, that the need for a new 
textbook of the subject in the English language has been much felt. 
Professor Iddings’ book is in some ways not unlike the well-known 
Rosenbusch Iddings’, which has served the needs of several genera- 
tions of students. It is really, however, a new work, as a very 
excellent introductory or general part has been provided in which the 
chemical, physical, and optical properties of minerals are described, 
while the second or descriptive part is entirely remodelled and brought 
up to date. It is not difficult to trace the influence of certain standard 
authors in the treatment of some parts of the subject; more especially 
that of Professor Groth in the chapters on optical properties, and of 
Professor Rosenbusch in the special descriptions of the minerals. But 
the book has a marked individuality owing to the bright and interesting 
manner in which the author has handled his materials. It is brief, 
1 Geological Journal, 1903. 
