THE DIKES MAY BE ASCRIBED TO EARTHQUAKES. t35 



the fissures and perhaps out upon the surface; but the greater influence in 

 producing these results is to be accorded apparently to hydrostatic pressure. 



Phenomena commonly associated with Earthquakes. — The phenomena just 

 mentioned are such as are frequently associated with earthquakes. We are 

 all familiar with the fissures and craterlets of the late Charleston and 

 Sonora earthquakes, where the sand and water issued so copiously, in some 

 cases for several days' after the earthquake. But that we may not seem too 

 hasty in referring the sandstone dikes to earthquakes, let us examine the 

 records of such seismic movements and briefly note some of their effects. 



During the great Calabrian earthquake of 1783 many fissures were formed 

 in the ground, and from some of them great quantities of sand and water 

 issued. After the flow ceased the openings were left full of saud. In our own 

 country the fissures formed by the earthquake of Xew Madrid, Missouri, in 

 1811-1813, were still plainly visible in 1846 when Sir Charles Lyell visited 

 the scene. He says that they were often parallel, and yet there was con- 

 siderable diversity of direction, varying from 1ST. 10° to 45° W. Many 

 were yet traceable for half a mile and upwards. It is said that during 

 the earthquake, powerful jets of water filled with sand and coaly matter 

 issued from these fissures; and distinct traces of them could be seen after the 

 lapse of thirty-four years. Similar phenomena accompanied the earthquake 

 of 1819, at the mouth of the Indus. In all the cases already cited the 

 fissures were in unconsolidated material only. 



During the earthquake of Valparaiso in 1822, however, parallel fissures 

 were formed in the solid granite of the coast, and could be traced inland for 

 1 $ miles. Cones of sand 4 feet in height were formed in several districts 

 by the water, and sand forced up from below through the fissures to the sur- 

 face. More profound fractures were associated with the great earthquakes 

 of New Zealand in 1848 and 1855. After the first, a fissure averaging 18 

 inches in width could be traced sixty miles. At the time of the second, a 

 fault was formed with a displacement of nine feet, which could be traced for 

 a distance of ninety miles. 



At the time of the Sonora earthquake, May 3, 1887, there were, accord- 

 ing to Mr. Goodfellow,* extensive irruptions of water and sand from the 

 fissures formed in connection with the earthquake. These fissures could be 

 traced more or less continuously for a distance of fifty miles. They mark 

 the line of a fault, the average displacement of which for the whole distance 

 was eight feet. It is inconceivable that such profound fractures should 

 affect the thin covering of soil only ; they must extend as well into the solid 

 rock beneath. 



The fissures and craterlets formed in connection with the Charleston earth- 



* Science, Aug. 12, 1887, vol. X, p. 81. 

 LVII— Bum,. Geol. Soc. Am., Vol. 1, 1H89. 



