PETROLOGICAL ABSTRACTS AND REVIEWS 471 
The crossing of the Rondout Valley has proved one of the most 
‘serious difficulties encountered in the whole work, and very detailed 
study has been given it. This valley is four miles wide and heavily 
drift covered, and the author was given the problem of deciding on the 
possibility of driving a pressure tunnel, together with the best place and 
most favorable depth for such a work. ‘This required the determination 
of the topography of the buried valley floor; the position, within five 
feet at any given point, of any one of the twelve irregularly dipping 
and faulted formations in this valley; the structural and petrologic con- 
dition of each, with regard to porosity; and a study of the underground 
water circulation. While frequent recourse was had, of necessity, to 
diamond drilling, it was of course very important to determine which 
sections might safely be left without testing in this expensive and 
tedious manner. It was decided that the limestones must be avoided, 
because of their liability to solution by water under such great head, and 
likewise a heavy but brittle grit, because of the free circulation through 
it. Under this general type fall most of the other problems, which are 
concerned largely with the crossing of these old buried valleys. In 
New York City itself, however, some interesting complications are 
introduced by the value of the ground, the heavy traffic, etc. 
-It is impossible in this review to do more than give a general idea 
of the type of problems encountered; the practical value of the book 
lies in its complete presentation of the data at hand, and its faithful 
delineation of the lines of reasoning followed. The numerous and excel- 
lent plates and figures greatly clarify the text and enhance its interest. 
There seems little doubt that such geological work will come more and 
more into demand as its real value becomes recognized by engineers, 
and it is fortunate that one of the pioneers has been able in this report 
to sum up his experience and evaluate the various methods of attack. 
The author is to be congratulated, not only upon the success which later 
explorations have conferred upon his geological predictions, but upon the 
wisdom which he has displayed in presenting his report in so efficient 
and timely a manner. 
G. S. ROGERS 
Daty, REGINALD A. ‘The Nature of Volcanic Action,” Proc. 
Amer. Acad. Arts and Sci., XLVII (1911), 3, pp. 47-122. 
In this highly suggestive paper Professor Daly has summed up and 
correlated a large part of his researches and speculations upon igneous 
rocks into a systematic hypothesis of volcanic action. The paper is an 
attempt to present a working hypothesis of vulcanism which will “co- 
