806 



DYNAMICAL GEOLOGY. 



uary, 1869, in Cachar, India, about 30 miles. Lasaulx determined for 

 the same in the case of an earthquake near Aix-la-Chapelle (Aachen) 

 in June, 1877, about 16*85 miles ; and for that of another in the same 

 region in 1873, a position toward the base of the supercrust (p. 147); 

 but his results have been questioned. 



The noted earthquake of Calabria commenced its shocks in 1783, 

 and continued them to the close of 1786; 949 were counted in 1783, 

 and 151 in the following year, more than half of which were of great 

 violence ; they were felt through Sicily and as far north as Naples, 

 but the region over which they " excited intense alarm did not gener- 

 ally exceed 500 square miles in area." 



Henry D. Rogers, many years since, showed that the earthquake of 

 the 4th of January, 1843, traversed the United States from its north- 

 western military posts, beyond the Mississippi, to Georgia and South 

 Carolina, along an east-southeast course, Natchez lying on the south- 

 ern border, and Iowa about the northern ; and made out for the rate 

 of travel, thirty-two to thirty -four miles a minute. 



The principal geological effects of modern earthquakes come through 

 the forced or translation waves they make in the ocean, as explained 

 on page 679. The minor effects are: (1) the displacement of loose 

 rocks ; (2) destruction of life in the sea, on the same principle that a 

 blow on the ice of a pond will stun or kill the fish in the waters be- 

 neath ; (3) destruction of life on the land. Destruction of cities and 

 of human life have been too often recounted to need special illustration 

 in this place. The great fractures and the changes of level often con- 

 nected with them have a place, for the most part, among causes rather 

 than effects. In times of mountain-making, when faults thousands of 

 feet in depth were made, each at successive shoves, if not abruptly, the 

 destruction to life may have been almost world-wide. The waves 

 made in the air, or sound-waves, are part of the sensational effects of 

 earthquakes. 



The great depth of some earthquake centres favors the conclusion 

 that the earth's volcanic and mountain-making operations have ordi- 

 narily affected subterranean regions far below the limit of the super- 

 crust. 



4. Inequilateral Character of Mountains. 



The succession of flexures which make up some mountain ranges, 

 from one side to the other, are evidence that the force producing the 

 upturning acted laterally. 



The additional fact that these flexures, as a general thing, have, in 

 mountains like the Appalachians, an inequilateral character, with the 

 steeper slopes facing the same way (p. 788), proves that the lateral 



