291 
of Edinburgh, Session 1880 - 81 . 
island, human habitations and other structures below low water of 
spring tides ” (“ Journal of the Royal Geological Society of 
Ireland for 1880,” vol. v. p. 180). 
(4.) Reference has been made to “ Rockall which at present con- 
sists of only one rocky peak. But a chart exists dated in 1634,'* 
which represents the place as consisting of two islets, a larger and a 
smaller, hut the smaller is now exposed to view only at half tide,f 
suggesting subsidence. 
(5.) Another discovery recently made, is the finding in several 
parts of the North Atlantic, molluscs which betoken littoral conditions. 
Thus on the Porcupine Bank — a shoal situated about 120 miles 
west of Galway (Ireland), a specimen of “ Litorina litorea ” was 
dredged up, with regard to which Professor King of Queen’s College, 
Ireland, asks, “ How has this shell, which lives between ordinary 
tide marks, got into 80 or 90 fathoms of water, and at a distance of 
120 miles from the shore ?”f 
A similar case occurs in a part of the North Atlantic, about half- 
way between the south end of Greenland and Rockall, where a 
number of star-fish were brought up by the sounding line from the 
sea bed at a depth of 748 fathoms. Dr Wallich, in the “ Bull 
Dog” surveying ship, employed in 1860 to make these soundings, 
drew out an exceedingly interesting memoir J (published by the 
Admiralty), in which he gives his “reasons for believing that 
although originally a shallow -water species, these star-fishes had 
gradually, and through a long series of generations, accommodated 
themselves to the abnormal conditions incident on the subsidence 
of the sea heel” (“Memoir,” p. 141). 
Dr Wallich further observes, that “ no proof of subsidence could 
he more complete, than the detection of a colony of acclimatised 
star-fishes belonging to a species typical of the Boreal province, well 
known to range from the confines of the Arctic circle to our own 
shores, and shown to have accommodated themselves to a depth of 
200 fathoms without variation ; whilst the fact of subsidence being 
* The chart alluded to is a French navigating chart, of which a copy is 
given in the 5tli volume of the Eoyal Irish Geological Society. 
f “ Eeport of Soundings by H.M.S. 4 Porcupine ’ in 1862.” 
+ “North Atlantic Sea-bed,” by G. C. Wallich, F.L.S. and F. G.S., 
naturalist to expedition under Sir F. L. M ‘Lintock, “to survey the proposed 
North Atlantic route for a telegraphic wire between Great Britain and 
America.” 
