405 
and in tlie North Atlantic. For the present there will only be 
laid stress on investigating the foundation of these hypotheses: if 
the foiind shells really may be supposed to have been outside the 
vertical range of their respective species. Then Professor Brøggers 
hypothesis on a sinking of the submarine „Continental platform” is 
to be discussed, as far as this is based on the appearance of 
shallow - water shells at greater depths than those at which the 
species are living. 
In ,^Ann. ^ Mag. Nat. 1868 Jeffreys sets forth a hypo¬ 
thesis on a former sinking of the seabed off the Shetiand Isles. He writes 
concerning this as follows (p. 304): — „Semifossil shells of arctic 
species (such as Pecten islandicus, Tellina calcarea, Mya truncata, 
var. Uddevallensis, Molleria costulata, Trochus cinereus, and Trophon 
clathratus) are raet with on the sea bottom at considerable depths, 
and at some distance from land. The only explanation I can offer 
is a former elevation of the sea-bed whereon these molluscs lived (and 
which was probably in shallow-water), and its conversion into dry land, 
and a subsequent subsidence. Perhaps the seabed is still sinking”. 
Among the dead shells which, according to Jeffreys, have been 
found here at greater depths than those in which the species are 
still living in more Northern latitudes Pecten islandicus is specially 
to be noted. This shell was dredged in the Shetiand seas at depths 
varying from 75 to 170 fathoms, which — compared with the sub- 
joined statements about its vertical distribution at the present 
time — seems to be 50 to 100 fathoms below the level on which 
the animal lives in the North-Atlantic and the North Polar Basin. 
Vertical distribution of Pecten islandicus: 
10—50 fms., off the Northern coasts of Norway (G. O Sars 1878). 
37—88 fms., the Barents-Sea (v. Noman 1881). 
6—60 fms., Kara-Sea (Leche 1878, Collin 1887). 
40—147 fms., Greenland-Sea (Grieg & Friele 1901). 
5—55 fms., off the East-coast of Iceland (the author, referring 
to „Diana”s dredgings in 1900). 
