REVIEWS 759 
It is his view that ‘‘the establishment of a genetic classification is dependent 
only on a fuller knowledge of facts and principles,” and ‘‘a systematic 
treatment of igneous rocks on these lines . . . . is not to be expected in 
the immediate future.’’ Professor Iddings has made no attempt at a 
genetic classification, believing that there are too many factors influencing 
genetic relations to permit of their use. He thinks that the chemical 
composition of an igneous rock is “‘its most fundamental character . 
and is therefore of greatest importance for its correlation with other igneous 
rocks.” 
Professor Iddings’ book is a most valuable addition to the literature 
of petrology and will be welcomed by students for its presentation of the 
new view of those problems which, to a large extent, have heretofore been 
given only in scattered publications, representing the work of such men 
as Day and his colleagues in the Geophysical Laboratory, Doelter, and 
Vogt. 
The book is well printed on good paper, the half-tones are clear, and 
the line drawings are neat. The book is bound in blue cloth uniformly 
with the same author’s Rock Minerals. 
gels 
Through the Yukon and Alaska. By T. A. Rickarp. J-XIII, pp. 
384. San Francisco: Mining and Scientific Press, 1909. 
Few if any travelers in Alaska have made so many and such accurate 
observations as Mr. Rickard, and of those who have published similar 
journals, no one has included so much of real value to those interested 
in the resources of the Yukon district and Alaska, or in the mining activi- 
ties of those countries. The author has told in a delightful way many 
of the incidents of travel, and has taken pains to give accurately the 
history of some of the most remarkable discoveries in these northern 
countries. The romantic history of the Treadwell mines, the discovery — 
of gold on the Klondike, the wonderful development at Fairbanks, and the 
story of the discovery and exploitation of the Nome beach, are here given 
in a fuller and more interesting way than they have elsewhere appeared. 
Mr. Rickard has retold many of the stories associated with life in Alaska, 
during the exciting periods from 1895 to 1900: thus the fake discovery of 
a Silent City, the story of Soapy Smith and his gang of desperadoes, the 
incidents associated with the great stampede over White Pass and Chilcoot 
Pass, the life at Dawson, on Cleary Creek, and the story of many events 
at Nome which have afforded material for novels and magazine articles, 
are given in a very readable form. The book is, however, more than a 
