378 Prof. G. A. J. Cole— Rocks and their Origim. 



explanation of the origin of tlie disturbances. A study of their 

 distribution shows that, while some earthquakes are more or less 

 directly connected with volcanoes, active or dormant, others, including 

 the more important and destructive, happen in districts remote from 

 modern volcanic action. ' Destructive earthquakes occur on " the 

 steeply sloping ocean-bed to the east of the Japanese empire. In 

 the same way, the disastrous earthquakes of South America originate 

 beneath the Pacific Ocean, in districts that are distant many miles 

 from the volcanic vents of the Andean chain. The great earthquakes 

 of India and Turkestan, again, occur in countries from which volcanic 

 action is now entirely absent, but which lie on the steep sides of 

 mountain ranges that are known to be of recent growth ". 



Earthquake shocks are of all degrees of intensity, from mere 

 tremors to those which affect areas of nearly two million square 

 miles, although, whether weak or strong, it is considered that, as a 

 general rule, the centre of the disturbance is not more than a few 

 miles below the surface. 



In considering the folding and fracturing of the rocks forming the 

 earth's crust, the author remarks that the folding would take place 

 slowly, until it gave place to fracturing and faulting. Fractures 

 would appear on the surfaces of folded rocks, and some earthquakes 

 maj- be attributed to such causes ; but it is regarded as more probable 

 that they are caused by the abrupt and violent process of faulting. 

 The author's principal object is " to show that the great majority of 

 earthquakes are due to the intermittent growth of faults, that, when 

 a displacement occurs at some depth, the friction generated by the 

 sudden sliding of one huge rock-mass over and against the other must 

 produce an intense jar in the solid crust around, a series of vibrations 

 which, propagated outwards in all directions, gives rise at the 

 surface to an earthquake shock ; and that, in those somewhat rare 

 cases in which the displacement is continued right up to the surface, 

 the sudden spring of the displaced crust must complicate and increase 

 the shock due to the grating of the sliding masses". 



The phenomena observed in connexion with earthquakes, simple, 

 twin and complex, in various parts of the world, the formation of 

 fault-scarps, and other features, are duly described; and references 

 are given to the leading publications on tlie subject. 



IV. — Rocks and their Origins. By Grenville A. J. Cole, Professor 

 of Geology in the Royal College of Science for Ireland. 8vo; 

 pp. viii, 175, with 20 text-illustrations. Cambridge: at the 

 University Press, 1912. Price \s. net. 



IN this little volume, issued as one of "The Cambridge Manuals 

 of Science and Literature ", the author deals with the method of 

 formation of limestones ; sandstones ; clays, shales, and slates ; 

 igneous and metamorphic rocks. Some attention is given to the 

 colours of the rocks, and their soils, and more to the varied forms of 

 scenery to which they give rise : a subject treated in most of the 

 illustrations, among which the quartzite cone of Croagh Patrick is 

 an example. It is needless to say that the volume is clearly and 



