132 Reviews — Professor W. H. Hobbs on Earthquakes. 



how the gi'eat earthquakes studied in recent years — the Mino-Owari 

 (Japanese) earthquake of 1891, the Assam (Indian) earthquake of 

 1897, the Owens Valley (Sierra Nevada) earthquake of 1872, the 

 Sonora (Mexican) earthquake of 1887, the Yukutat (Alaska) earth- 

 quake of 1899, and the St. Francisco (Californian) earthquake of 

 1906 — were all accompanied by manifest dislocations at the earth's 

 surface along lines of fault. 



But in addition to this connexion between great lines of faulting 

 and the occurrence of eai'thquake shocks — a connexion now generally 

 accepted by geologists as definitely proved — the author, following 

 up and extending the recent work of De Montessus, argues that 

 innumerable lines of minor strain and fracture (' seismotectonic 

 lines ') can be detected by means of a study of dislocations on railways, 

 the occurrence of ' craterlets,' and similar evidences of surface 

 disturbance. The manner in which this kind of evidence is employed 

 in seismological investigation has been illustrated in the case of the 

 Charlestown earthquake by a paper published by Professor Hobbs in 

 the Geological Magazine (May, 1907, Dec. V, Vol. IV, p. 197). 

 The results obtained are networks of intersecting lines, which can 

 often be shown to coincide with the existing features (' lineaments') 

 of the district. Examples of ' seismotectonic maps ' constructed on 

 this principle are given in chapters vi and vii, including Ischia, 

 Japan, California, the Greater Antilles, Scotland, the eastern United 

 States, the Charleston area, etc., and the existence of such minor 

 lines and their connexion with the surface features of the distiict 

 is a question well worthy of the consideration of all geologists. 



Chapters viii to xii, giving clear but condensed accounts of great 

 earthquakes, especially those of the United States, cannot fail to 

 prove of great service to all students of the subject. The essential 

 and significant details are admirably sifted out from the often confused, 

 trivial, and irrelevant materials of the original descriptions ; and many 

 subjects, like the modifications produced in the flow of undergound 

 waters, and the emission of ' sulphurous vapours,' with other minor 

 phenomena, receive judicious treatment. The same praise may be 

 awarded to the chapters dealing with the modes of studying the 

 evidences of disturbance by earthquakes on the land and beneath the 

 sea (chapters xiv and xv). 



It is only after the geological aspects of the subject have been fully 

 discussed that the author comes to the study of earthquakes by 

 instrumental means, and proceeds to the discussion of the principles, the 

 construction, and the modes of use of seismoscopes, seismometers, and 

 seismographs. The reader will find in chapter xvi a very intelligible 

 account of all the moi'e recently invented types of apparatus now 

 employed in the study of earthquakes. In his remarks on the 

 relative values and applicability to different conditions of the various 

 instruments, there is one very important point which has been 

 overlooked by the author. As he justly states, all forms of 

 seismograph suffer, and always must suffer, under the disadvantage 

 that pendulums of every kind have a vibration of their own, dependent 

 upon their length, and hence the movement of the earth's surface is 

 complicated with that proper to the pendulum. By the employment 



