SILICIOITS SPRINGS. 



183 



the depth of a foot and upward. The strata are 

 neaily always parallel and horizontal, though some- 

 limes slightly undulating. The silex forms sta- 

 lactites, often two inches in length, in the crevices 

 of the silicious deposites, and these are frequently 

 covered with small, brilliant quartz crystals. Com- 

 pact masses of silicious deposites, broken by vari- 

 ous causes, have been re-cemented by silica, and 

 the compound is represented as very beautiful. 

 Some of the elevations of this rock or breccia are 

 upward of thirty feet in height. 



The general deposite appears to be considerable, 

 and to form low hills. The colours of the clay 

 and silicious substances are very various, and even 

 brilliant; white, red, brown, yellow, and purple be- 

 ing the principal tints. Where the acid vapours 

 reach the rocks, they deprive them of their colours. 

 Sulphur is abundant, and the springs occur in a dis- 

 trict of lava and trachyte.* It is highly probable, 

 that in a region of submarine volcanoes, the springs 

 which boil up into the ocean from the bowels of 

 the earth are so saturated with sihcious matter as 

 to form extensive deposites far and wide over the 

 bed of the sea ; and there becoming interstratified 

 with shelly and calcareous deposites, may form the 

 substratum or foundation on which coral animal- 

 cules rear heir gigantic structures. 



Ferruginous Springs. — More or less iron is held in 

 solution by nearly all springs, and often in such 

 quantity as to stain the rocks or herbage through 

 which the waters flow, and serving to bind together 

 sand and gravel into solid masses. There can be 

 no doubt that iron is conveyed in considerable 

 quantities from the interior of the earth into lakes 

 and seas, and there acts as a colouring and cement- 

 ing principle among the silicious and carbonaceous 

 deposites which are continually forming. We have 



♦ Edinburgh Phil. Journal, vol. vi., p. 306. 



