THE VOYAGE OF H.M.S. CHALLENGER. 
26 
SlX*CA OX Till 
Menu MCA i. 
Aenux or Water. 
Sexeca ox the 
L c< el or the 
Oceax. 
' 'iiK timfs fur from their place of origin. All rocks, even the hardest, are penetrated 
I y w ter. which dissolves them, at least partially. Seneca attributes this solvent 
;k rion to the presence of a gas (spiritual). Thermal springs possess the power of 
m>-s< 'vit.g minerals in the highest degree, and among those which offer least resistance he 
< m n. rates salt, sulphur, nitre, alum, bitumen, and lime. The matters dissolved by 
\.;m i are <lep. -sited again, and this precipitation is especially abundant when the waters 
!■•■ tl rn md gaseous. He likewise explains the formation of calcareous tuffs, and 
[■'■lets out that the saline substances held in solution by the aqueous element maybe 
a! or; d by earthy layers, which, in a way, serve as a natural filter. What has been said 
ihove r K>n the chemical action of water shows that Seneca had clearly recognised those 
hydrothermic phenomena which play so important a role in geology. 1 
H ideas concerning the mechanical action of water are not less just. The hardest 
ro ks cannot resist the destructive effect of a repeated dropping of water, and the 
erosive effects of water are most pronounced when the forces in play are those of 
ir :ims, urrents, and the waves of the sea, as may be observed in the beds of rivers 
d on bold coasts. Everywhere water is seen victoriously attacking and destroying 
■ k . tin chemical effects often precede the mechanical. Streams and rivers at all times, 
• especially during floods, transport clay, sand, and rocks, picked up from the layers 
v l . I 'key t -avers.’. The erosive power of waves is, however, even greater than that of 
r lining water; elitfs broken and smashed into ruins testify to the work of destruction 
effe t-d by the sea on coasts. Rivers deposit at their mouths the matter which they 
■ nr in suspension, thus forming deltas. In their turn the mineral particles in 
.)-!>• U'ion in marine waters are deposited at the bottom of the sea, often at considerable 
m ■ from the coasts. Among the agents which take part in marine sedimentation, 
t: k - and currents are enumerated. Seneca points out that all waters, and especially 
th< *.*■■<• '»f the ocean, possess the power of clearing themselves from all impurities ; they may, 
in* E d, 1" said to wash the shores and lay down near them all matters in suspen- 
-> tliit in the course of centuries the lines of coasts undergo sensible modifications. 
Tt urface of the ocean is spherical ; its level remains constant in spite of the continuous 
"ii of river water, nor does the latter modify the saline taste of the sea, and he 
at t r l»ut<- this constancy in level and saltness to evaporation. At certain intervals, 
i; .V'-v- the normal height of the ocean undergoes a general but temporary elevation, 
i oxhif mg i i. luges with a sort of periodicity, and causing profound modifications on 
'! • -ur r. of the globe. These diluvial inundations do not, however, spread over the whole 
’•'•uid only >me regions arc thus invaded. Such great phenomena cannot be referred 
t<> a . • glo c : i . ; several must unite to produce them, as torrents of rain, earthquakes, 
-lid p* rhaj.s other causes. The waters of the sea might easily cover the highest moun- 
r 1 r,:., , I »;• :•« i , i hen AnKhatmngen ties PbiloBophen Seneca, Wolfenbuttel, 1873 and 1876, Thcil ii. 
n> lo-ia. 
