SILI€IOUS SPRINGS. 
18S 
tke depth of a foot and upward. The strata ar-e 
nearly always parallel and horizontal, though some- 
times shghtly 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, 
aJid to form low hills. The colours of the clay 
and silicious substances are very various, and even 
brilhant ; 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 silicious 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 their gigantic structures. 
Ferruginous Spings.—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. 
