424, Reviews—FPirsson’s Text-Book of Geology— 
Cornbrash and Kelloways rock of Yorkshire are not exactly con- 
temporaneous with the strata bearing the same names in the South of 
England, while the Grey Limestone series appears to belong to the 
Blagdeni zone of the southern district. 
The chapter on glacial deposits contains a clear and concise 
summary of Professor Kendall’s views on the modifications of the 
drainage system of the district during the Ice Age. These are 
accepted almost in their entirety, with the reservation that ‘‘in 
certain cases it may be questioned whether the existence of extra- 
morainic lakes can be proved, and whether the streams at the margin 
of the ice-sheet would not in themselves be sufficient to excavate the 
channels”. This is scarcely to be regarded as an improvement on 
the original theory: since one of the strongest arguments brought 
forward by Professor Bonney against the glacial origin of these 
channels is the difficulty of explaining how a stream whose position 
is determined by a necessarily shifting barrier like the edge of an ice- _ 
lobe could have excavated such clean-cut and steep-sided trenches. 
The chapter on economic geology affords somewhat melancholy 
reading, since it is in the main a record of extinct industries, such 
as the manufacture of alum and the working of jet; while, un- 
fortunately, the great ironstone beds of the Middle Lias of Cleveland 
thin out almost to nothing before they reach the boundaries of the 
area here described, and the Dogger or Top Seam is for the most 
part represented by sandstones. 
This memoir will be heartily welcomed by all who are already 
acquainted with the geological features of one of the most interesting 
districts in the kingdom, while those who wish to acquire this 
knowledge will find it a mine of accurate and clearly expressed 
information on all sides of the subject. | 
R. H. Rasratt. 
Il.—A Trxr-Boox or Grotoey. Part 1: Puysrcan Guotocy. By 
Louis V. Pirsson. pp. vili+ 444, with frontispiece, 317 figures 
in the text, and Geological Map of North America. New York, 
John Wiley & Sons, Inc.; London, Chapman & Hall, Ltd. 1915. 
Price 10s. net. 
'W\HIS treatise on geology will, on completion, consist of two parts, 
the first of which—the one now before us—is by the well-known 
professor of physical geology in the Sheffield School of Yale University, 
while the second, under the title of Historical Geology, is to be from 
the pen of his colleague in the chair of paleontology, Professor 
Charles Schuchert. Professor Pirsson tells us in his preface that it 
has been his aim to hold the balance even between physiography, 
which is the most popular side of the volume and the one most 
ordinarily studied, and the physical and chemical aspects, which form 
the real basis of the subject, and he has—we feel no hesitation in 
saying— successfully achieved his object. The task of the student of 
geology is akin to the detective’s; he has to take the evidence as set 
before him, and can rarely reconstruct past events. For thatreason, in 
geology theories have been put forward every whit as fantastic as ever 
