427 
If we regard the position of the stations, where tbe above 
named dead shallow water shells have been foimd, 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 
risiiig grounds which by a certain uniform rising of the sea-bed would 
turn into islands, and if living molluscs of the same species do not 
occur 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 ou very gentie slopes far from the coasts. Before 
mentioniug how the phenomenou 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 agendes 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 aloug 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 
in 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 
