390 Mr. Gwyn Jeffreys on Dredging among the Hebrides. 
cccasion, dredged them on the coasts of Skye and West Ross, 
at depths of from 30 to 60 fathoms, or 180-360 feet. They 
had a semifossilized appearance. Not one of the above-named 
species has ever, to the best of my knowledge and belief, been 
found in a living or recent state in any part of the British seas. 
All of them occur in post-tertiary or quarternary deposits on the 
west coast of Scotland, from a few feet above high-water mark* 
to 820 feet above the present level of the seat. The greatest 
subaérial height (320 feet) being added to the greatest submarine 
depth as above (360 feet), gives an extent of elevation and sub- 
sidence equal to 680 feet. But as Pecten Islandicus, for example, 
now inhabits the arctic ocean at depths varying from 5 to 150 
fathoms, let us take the average of these depths, viz. 774 fathoms 
or 465 feet, and add it tothe 680 feet. This would make 1145 
feet, and probably represent the height at which the sea-level 
may be supposed to have stood when P. Islandicus lived on 
the highest fossiliferous spot noticed by Mr. Watson. The 
non-fossiliferous boulder-clay, indicating the simultaneous pre- 
sence of arctic Jand which was also subject to glacial conditions, 
is stated by Mr. Watson { to be about 800 feet higher than the 
marine deposit. The height of the layer of sea-shells on Moel 
Tryfaen in Carnarvonshire (evidently the remains of an ancient 
beach) exceeds that of the similar deposit at Cardigan by more 
than 13800 feet ; and the difference of height observed in the 
case of other fossiliferous deposits in the north of England 
(e.g. Manchester and Kelsey Hill) shows that the disturbing 
movement has been unequal, and probably not synchronous, over 
the samearea. It would seem that the extent of such oscillation 
has not altogether amounted to 2000 feet in the British Isles, 
taking Moel Tryfaen as the greatest height, and the Shetland 
sea-bed as the greatest depth at which quaternary shells of 
recent species occur. The Scotch and Irish deposits, however, 
are on the whole far more ancient than those of Wales and 
England, judging from their geographical nature; the former 
are chiefly arctic, and the latter merely northern. Whether 
other parts of the North Atlantic sea-bed have undergone a 
much greater change of level since the tertiary epoch is not so well 
established. Dr. G. C. Wallich, in his admirable and philosophical 
treatise §, with which all marine zoologists and geologists are, or 
ought to be, familiar, believed that certain starfishes which he 
* British Association Report, 1862, Trans. Sect. p. 73 : Jeffreys, *‘ On an 
Ancient Sea-bed and Beach near Fort William, Inverness-shire.” 
+ Transactions of the Royal Society of Edinburgh, 1864, p. 526: Rev. 
R. B. Watson, “ On the Great Drift-beds with Shells m the South of Arran.” 
+t Loe. cit. p. 524. 
§ The North Atlantie Sea-bed, 1862. 
