ON DREDGING AMONG THE HEBRIDES. 189 



Watson* to be about 800 feet higher than the mean 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 iinequal, and pro- 

 bably 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 occiu-. 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. 

 WaUich, in his admirable and philosophical treatise t, with which all marine 

 zoologists and geologists are, or ought to be, familiar, believed that certain 

 starfishes which he had procured at a depth of 1260 fathoms (7560 feet) in 

 lat. 59° 27' N., long. 26° 41' W., about halfway between Cape Farewell and 

 the north-west coast of Ireland, were originally a shallow-water species, but 

 had gradually, and through a long course of generations, accommodated them- 

 selves to the abnormal conditions incident on the subsidence of the sea-bedj. 

 The starfishes in question, which he refers to the OpMocoma yramdata of 

 Forbes {Asterias nigra of 0. F. Miiller), appear, however, to belong to a diffe- 

 rent species, which inhabits deep water. In an important paper by Professor 

 Sars, on the distribution of animal life in the depths of the sea§ , he states 

 that Ojyhiocoma nigra (0. granulata, Forbes) is certainly found in shallow 

 water, viz. from 2 to 30 fathoms, on the coast of Norway, but never at a 

 greater depth so far as is yet known, and that it does not range north of the 

 firth of Drontheim. He is of opinion that Dr. Wallich's species is Ophiacantha 

 spinidosa of MiiUer and Troschel, a well-known and Groenlandic species, 

 which is not littoral, but rather a deep-water kind, viz. from 20 to 190 

 fathoms ; and he infers from Wallich's own account that the last-named 

 species, instead of Ophiocoma nigra or granulata, was the one taken by the 

 * Bulldog '-sounding in 1260''fathoms. Dr. Wallich also adduces his discovery, 

 at a depth of 682 fathoms (4092 feet), in lat. 63° 31' N., long. 13° 41' W., of 

 two testaceous Annelids, which he assumed to belong to " known shallow- 

 water forms," as further evidence of an extensive submergence of the North 

 Atlantic sea-bed. These Annelids were named by him Serpula vitrea and 

 Spirorhis naiitihides. But Professor Sars disputes their being shallow-water 

 species. The former he identifies with his Serpula polita ( = Placostegus 

 tridentatus, Fabricius) ; the latter is referred by Morchlj to the Serpula 

 spirorhis of Linne. The one is regarded by Sars as a deep-water and not 

 littoral species, being found on the Norwegian coast in 20-300 fathoms ; the 

 other has a wide bathymetrical range, from low-water mark to 300 fathoms. 

 I suspect, moreover, that there has been some mistake in the determination 

 of the Sjnrorbis, and that it belongs to another species than that to which 

 WaUich has assigned it. As to the accuracy of his statement that he pro- 



* Loc. cit. p. 524. 



t The North Atlantic Sea-bed, 1862. 

 \ Loc. cit. p. 41. 



§ Vid.-Selsk.Forhandl. 1864: Hr. Sars, " BemEerkninger over det djriske Livs Udbred- 

 ning i Havets Dybder." 



II Naturhist. Tidsskr. 1863 : " Kevisio critica Serpulidarum." 



