427 
If we regard the position of the stations, where the above 
named dead shallow water shells have been found, it will appear, 
that most of them are either placed on the banks or on the slopes 
of the ocean. In looking for a proof of a former sinking of the 
sea-bed it will be of peculiar interest to take notice of the oro- 
” graphical features of the finding place. If the shells are lying on 
rising grounds which by a certain uniform rising of the sea-bed would 
turn into islands, and if living molluses of the same species do not 
ocgur at present on a higher level on such banks in the sea, there 
would be much more reason to presume a sinking of the sea-bed 
" Than if they are found on steep slopes, and the same is the case 
if they occur on very gentle slopes far from the coasts. Before 
mentioning how the phenomenon most naturally is accounted for on 
the different tracts the means by which the dead shells are dis- 
persed will here briefly be discussed. 
The principal agencies which contribute to the dispersal of 
the shells are as follows: 
I. Marine surface currents. These transport a) floating ice, 
b) seaweeds on which molluscs are fixed, c) the molluscs 
themselves. 
II. Currents along the sea-bottom. 
III. The waves at precipitous coasts. 
IV. Animals (Sea-birds, Fishes, Pagures etc.). 
The transportation of shells by means of floating ice is treated 
page 397 to 399. The tracts where the above mentioned shallow- 
water shells have been found in the Atlantic and-in the Mediterranean 
lies, however, almost entirely out of reach of the floating ice of 
the present time. It is however granted that the floating ice earlier 
im post-tertiary time has reached much farther southward than at 
present. This being the case it can by no means be regarded as 
excluded, that a great deal of the littoral shells occurring far from 
the coast at considerable depth, e. g. between the Færoes and the 
