DELESSE—-SEAS OF THE OLD WORLD. 7 
gradually under the sea, forming a vast terrace, which is covered 
with sand; this is notably the case in the Gulf of Gabcs, where the 
sand extends to a distance of more than 200 kilometres from the 
shore. 
In the Mediterranean, certain submarine rocks reappear in the 
neighbourhood of the coasts, particularly when these are moun- 
tainous. Clay extends over large surfaces in the archipelago, in 
the Gulf of Syrte, in the south and to the east of Malta, in the 
Adriatic, round Italy, round the Baleares, and to the east of Spain. 
Although the Mediterranean contains a great abundance of mol- 
lusks, the deposits rich in shell-remains do not cover vast surfaces,— 
a circumstance which is apparently due to the fact ofits shores being 
generally steep. 
The Baltic is an inland sea, very shallow when compared with 
the seas of the south of Europe. Submarine rocks constitute a large 
portion of the bed of the Baltic, especially along the coasts of Sweden 
and Finland, as well as in the Gulf of Livonia. In the archipelago 
of Aland they even show a connexion with the granitic rocks which 
form the promontories of Stockholm and Finland. Clay occurs in 
nearly all the eastern Baltic, and it even extends over large surfaces 
there. It must no doubt be attributed to the argillaceous beds of 
the schistose Silurian series ; for this formation is strongly developed 
on the neighbouring shores, more especially in Sweden and Russia. 
Pebbles also form interrupted zones, which appear to range nearly 
parallel to the coast of Sweden; their mean depth is about 50 
metres, but towards the north it is much greater, so that the sea 
cannot now displace them. ‘They indicate, therefore, an unconsoli- 
dated deposit anterior to the existing epoch, and probably an ancient 
beach of the Baltic. 
Silt fills up several distinct basins; it follows at some distance the 
indentations of the coast-line, and again recedes round the islands. 
It fills up the central portions of the Baltic and of the Gulf of 
Bothnia, but not always the deepest parts. 
Sand forms large margins on the shores of the Baltic; it occupies 
also vast submarine surfaces, particularly off the coasts of Pomerania 
and Courland, in the Gulfs of Livonia and Finland, in the archipelago 
of Aland, and in the Gulf of Bothnia. The abundance of sand in the 
Baltic may be attributed to the circumstance that this sea is not 
deep, and that it receives numerous torrential rivers which are fre- 
quently swollen by melting snows, descending from Finland or 
the Scandinavian Alps after having swept over granitic rocks; it is 
owing especially to the fact that the rivers of Scandinavia, Russia, 
and the north of Germany descending into the Baltic flow through 
hydrographic basins covered by the diluvium of the north of Europe, 
which is essentially sandy. Mollusca are rare in the Baltic on ac- 
count of the very slight saltness of its waters. 
Let us now pass to the ocean, leaving tho seas of France and of 
the British Isles, which have been previously studied. 
The ocean is of great depth along the Iberian peninsula, and at 
a short distance from its banks. Submarine rocks indicate the con- 
