DYNAMICAL GEOLOGY. 285 



specific examples the frequency of earthquakes along narrow 

 tracts or over areas which have been the seat of important 

 crust-movements of displacement, fracture, or subsidence. 

 Toula proposed the distinctive name of "dislocation earth- 

 quakes" to such as accompanied the grander movements in 

 the earth's crust. 



Gilbert in California, Griesbach in Beloochistan, Koto in 

 Japan, and other observers have proved the origin of extensive 

 fissures at the earth's surface as a consequence of recent 

 earthquakes. Permanent changes in the surface conformation, 

 especially subsidences, have very often been reported as a 

 chief factor in the catastrophes caused by earthquakes. In 

 the fearful earthquake at Lisbon, the quay sank into 

 the sea with all the ships anchored in it and thousands of 

 people on its margin. During the Calabrian earthquake, in 

 the year 1/83, more than two hundred lakes and morasses 

 were formed. In the year 1819, according to Lyell, an 

 earthquake at the eastern river-mouth of the Indus converted 

 an area 2000 square miles in extent into a lake ; on the 

 Mississippi flats, in China, Syria, and Chili, earthquake 

 inthrows have been recorded. 



It has, however, rarely happened that the ground has been 

 elevated in consequence of the passage of an earthquake. 

 The best known accounts of elevations come from Chili, and 

 were accepted as trustworthy by no less an authority than 

 Charles Darwin ; Professor Suess regards them as of doubtful 

 integrity, and C. W. Fuchs affirms that since earthquakes and 

 their phenomena and consequences have been observed with 

 scientific accuracy, not a single case of ground-elevation has 

 been authoritatively recorded. 



G. Secular Movements of Upheaval and Depression. The 

 study of the sedimentary deposits of past geological epochs 

 reveals conclusively that vast changes have repeatedly taken 

 place in the distribution of land and sea upon the face of the 

 earth. But it is difficult to determine what changes are now 

 in progress, whether certain parts of the earth's land surfaces 

 are being at present elevated or depressed, or whether oceanic 

 variations are accomplishing changes in the relative level of 

 land and sea. It seems almost impossible to record slow 

 movements in the interior of the continents, and the 

 topographical maps render little assistance in this respect, as 



