492 SCIENCE PROGRESS 



made by these processes upon the surface Uneaments of the earth. The 

 planetesimal hypothesis does not provide for any molten igneous masses, 

 save the unsatisfactory " radial threads " of ChamberUn. "We begin to part 

 company with Prof. Hobbs, however, when he derives pockets of igneous 

 magma from the fusion of shale due to relief of pressure in the crust consequent 

 upon earth movements. He relies on a rather specious resemblance in 

 chemical composition between the average igneous rock and the average shale, 

 neither of which are very satisfactory entities. The greatest bodies of 

 igneous rock are the enormous basalt floods which cover areas of the order 

 of hundreds of thousands of square miles in various parts of the world, and 

 the huge granodiorite or granite batholiths of Cordilleran regions, neither of 

 which have the slightest affinity to, nor could have been derived from, fused 

 shale. Nor does the theory explain why the basalt floods are associated with 

 major vertical block movements of the earth's crust, and the acid batholiths 

 with relatively narrow belts of folding. 



The next section of the book deals with the changes of figure through 

 which the earth has passed. Prof. Hobbs supports the theory that the dis- 

 position of the main earth features is dependent upon tetrahedral deforma- 

 tion. In this the greatest strains occur in the zones separating rising and 

 sinking sectors ; and this leads to the consideration of the present-day regions 

 of greatest change, indicated by the distribution of earthquakes, volcanoes, 

 and young fold mountains. In this connection an instructive contrast is 

 developed between the " live " Pacific and the " dead " Atlantic coasts of the 

 two Americas. The uprise of the Cordilleras bordering the Pacific Ocean is 

 held to be due to lateral thrust from the subsiding ocean floor. It would be 

 interesting to learn whether all this could be squared with Wegener's theory of 

 continental drift, but Prof. Hobbs does not mention Wegener. 



In opposition to the prevalent Suessian conception, Prof. Hobbs develops 

 the view that underthrust from sinking areas, rather than overthrust from 

 rising land masses, is responsible for the overturning of folds, the accurate 

 outlines of fold mountains, and their tendency to present an apparently 

 advancing front towards adjacent sinking areas, generally oceans. 



Remaining chapters have the intriguing titles, " The Patterns of the 

 Facial Wrinkles," " The Design of the Fracture Marquetry," and " Lava 

 Composition in Relation to Earth Physiognomy." Notwithstanding one or 

 two points in which theory has overrun corroborative facts. Prof. Hobbs 

 has produced an extremely suggestive and thought-provoldng book, which 

 will help the advanced student and research worker to formulate more clearly 

 his own conceptions of the greater earth problems. 



G. W. T. 



Graphical and Tabular Methods in Crystallography. By T. V. Barker, M.A., 

 B.Sc, F.C.S. [Pp. ix + 152.] (London : Thomas Murby & Co. 

 Price 145. net.) 



The geometrical or goniometrical study of crystals, which forms the subject- 

 matter of this book, has not often been treated from such a utilitarian point of 

 view. Mineralogists have often spent hours trying to identify faces hitherto 

 unmentioned in the standard works, but although collected data of this 

 description may serve their purpose, we have now to consider merely a means 

 of identification in view of the ever-increasing number of crystalline organic 

 compounds. 



The author gives a critical selection of exact graphical methods found by 

 experience to be most adequate, with a brief theoretical explanation, and 

 finally outlines his ideal system of investigating and describing a crystal. 

 Fortunately, perhaps, the details are not original, for the suggestions are 

 based chiefly on well-known methods which, however, have never been 

 generally adopted. We are indebted to the author for many abstracts from 



