390 Mr. Gwyn Jeffreys on Dredging among the Hebrides. 



occasion, 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 behef, 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 320 feet above the present level of the seaf. The greatest 

 subaerial 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. 77^ fathoms 

 or 465 feet, and add it to the 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 land 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 1300 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 same area. 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." 



t Transactions of the Royal Society of Edinburgh, 1864, p. 526 : Rev. 

 R. B.Watson, " On the Great Drift-beds with Shells in the South of Arran." 



X hoc. cit. p. 624. 



§ The North Atlantic Sea-bed, 1862. 



