THE VOYAGE OF H.M.S. CHALLENGER. 
xviii 
jnroater than tliat of rimnins: water : cliffs broken and smashed into ruins are 
unquestioned witnesses of the work of destruction effected by the sea on coasts. 
Running waters deposit at their mouths the matters which they carry in suspension, 
thus fonning the deltas of rivers. In their turn the mineral particles in suspension 
in marine waters are deposited at the bottom of the sea, often at considerable distances 
from the cojusts. Among the factors which play a part in marine sedimentation, tides 
and currents arc enumerated. Seneca points out, besides, that all waters, and especially 
tliose of the ocean, possess the power of cleansing themselves from all impurities ; they 
may l>e said to wash the coasts and lay down near them all matters ' in suspension. 
Duriii" a series of centuries the lines of coasts undergo sensible modifications.^ 
A few notions regarding the geological action of water, the sediments carried into the 
sea and then solidified, are met with in the works of Kazwini,^ and other Arab writers. 
We find in Macoudi® examples of the carriage of fluviatile sediments, whose 
accumulation eau.ses the sea to retire. He had been profoundly impressed by the 
sanding up produced by the Tigris and Euphrates ; he cites the case of the city of 
Iliza, formerly a sea-port, which, after the lapse of 300 years, was situated far in 
the interior.^ 
.Mbirouni® embraced the idea, previously expressed by Megasthenes, according to 
which Bengal has been formed by the accumulation of sediment deposited by the Ganges. 
The writings of this author also show that he had observed the distribution of materials 
tninsported by water ; he points out that the larger fragments are deposited at the 
upper parts of rivers, that gravel is found lower down in their course, and finally, 
that sand and the finest particles are carried into the ocean. 
In Italy, in the fifteenth century, Leonardo da Vinci wrote that the sea changes the 
equilibrium of the earth, that the shells accumulated in various layers have necessarily 
lived on the spot which the sea occupied. The great rivers, he says, carry into the 
ocean the waste of the land, and the deposits thus formed have been successively covered 
by others of various thicknesses, and finally the bottom of the sea has become the top 
of mountains.® 
The Dane, Steno^, endeavours to show that the carapaces of Crustacea are formed of 
matter secreted by the animal’s body; he establishes the connection existing between 
fossils and the sclimentary layers which contain them, and the true origin of both. He 
was the first to distingui.sh the layers formed in the sea from those deposited in fresh 
water, and to notice the character of the .shells in both instances. He concludes, from 
• S« A. NebriuK, Die msologi«:hen Anachauungen des Philosophen Seneca, Wolfcnbiittel, 1873 and 1876. 
• Flouriahc**! aUjut 1263 a.d. * Flouri»hed about 91.1 A.D. 
‘ M»g>ndi, lAf Prairie* d’Or, texte et traduct. par MM. Meynard et Courtcille, Paris 1861 ; see in jiarticular the 
ancolot* of Kaled and AW-el-Mc^h, tom. i. c. ix. pp. 216, 222. ® Flourished about 1000 A.n. 
• See Venturi, £>«ai iur le* ouvmgcs physico-niath(funati(iucs de Leonard da Vinci, Paris, 1797. 
^ L>e aolido inlra tolidum naturaliter contento di“scrtationis prodromus, Florence, 1GG9. 
