434 
simple and natural. (I beg to observe that I have here only men- 
tioned the principal means of transportation.) 
I. The North Polar Basin (off Spitzbergen, between Jan 
Mayen and Spitzbergen, between Jan Mayen and Iceland). The 
shallow-water shells have been carried out by floating ice. 
A higher temperature of earlier date in post-tertiary time may also 
possibly have effected that some species (e. g. Saxicava arctica 
and Tellina calcarea) have formerly reached greater depths than at 
the present time. 
II. The Davis Strait and the Atlantic South of 
Greenland: Transportation by floating Ice. 
III. The steep slopes off the Norwegian coasts, at the 
horders of the Atlantic from the Færoes to Soudan, in 
the Mediterranean off the northern coasts of Africa, off 
the Azores, from off Nova Scotia to off Cape Hatte ras: 
in most cases transportation by currents. 
In the tracts named below the shell-deposits have hitherto 
been too little investigated as to give any exact idea from where 
the dead shallow-water shells at comparatively great depths origi- 
nate. It is to be hoped that renewed researches should be taken 
up with the special object to settie, in each single case, how the 
phenomenon is to be explained. 
I. The banks off the Norwegian coasts. It has not 
yet been thoroughly investigated if on these banks at a depth of 
50 to 100 fms. considerable quantities of shells from the tract be¬ 
tween tide-marks and the Laminarian-zone are deposited. 
IL The banks off the Færoes. The number of supposed 
shallow-water shells which have been found here at a depth of 
about 150 fms. is rather considerable. At present we do not know, 
however, whether the species which occur here in the greatest 
abundance, as Arca tetragona and Pectunculus glycemeris, in the 
Atlantic reach a depth of 150 fms. or not. 
