REVIEWS 671 



essentially straight lines which bear some relationship to geologic boundaries, 

 coast lines, mountain borders, etc., which are parallel to one another in 

 series, and which often intersect volcanic vents. Seismic intensity does not 

 vary with distance from any point or points within the earth, but is greatest 

 at or near the intersections of these seismotectonic lines. In only a very 

 few cases can seisms be said to owe their origin to vulcanism; the great 

 majority of shocks are due to faulting of the normal type and it is along 

 fractures that the earth-waves are propagated. Places situated even a 

 short distance from fracture hues along which disturbances have repeatedly 

 occurred have escaped serious injury. It is interesting to note also that 

 brontidi, the deep rumblings heard commonly in certain localities, occur on 

 lines along which much seismic disturbance has taken place, indicating 

 that these noises are due to slipping along fracture planes. A survey of 

 recorded earthquake scarps and fissures seems to show that notable surface 

 dislocations are formed only at times of notable shocks; that they are sharply 

 divided into two orders of magnitude; that the faults are of the nearly verti- 

 cal normal type, and that all the movements are due to an adjustment in 

 position of individual blocks. Thus a careful study of the earth movements 

 of a region may furnish data from which the position of otherwise unde- 

 terminable fault planes and systems may be derived. The topography 

 and hydrography of many areas is also modified along seismotectonic lines, 

 as is illustrated in the United States by the Northern and Southern Fall 

 lines, the Carolina coast line, the Connecticut line, and other lineaments. 

 The three most prominent seismic areas of the United States — the Atlantic 

 border, the middle Mississippi basin, and the bay of San Francisco — are 

 also sinking areas. Briefly stated, the law of the distribution of seismic 

 phenomena is that seismicity is localized along faults and is greatest at their 

 intersections. 



The second article deals more in detail with the southernmost portion of 

 the Italian peninsula and with the neighboring parts of Sicily, In this 

 region the relationship between the topography and crustal dislocations is 

 particularly well marked and the rectilinear stretches of coast are often lines 

 of great seismicity. Even the separation of Sicily from Calabria and 

 from Africa is a comparatively recent event due to subsidence along 

 fault planes. The well-known Italian volcanic vents are often situa- 

 ted at the intersections of fracture planes, while the destructive intensity 

 of Calabrian quakes is greatly augmented at similar points. A striking 

 fact in connection with the best-known earthquakes of Calabria is the 

 nearly constant relative intensity shown at a number of the affected com- 

 munes, indicating that these shocks have been the results of successive 



