Mr. Gwyn Jeffreys on Dredging among the Hebrides. 395 



stony, and never of soft ground, besides dead shells of the same 

 and similar species. That is more than twice the average depth 

 supposed by Professor Loven to be the limit of hard ground. 

 The Hebridean sea-bed, at very moderate depths (which Dr. 

 Wallich would call " shallow water "), mainly consists of a soft 

 and more or less tenacious mud, mixed M^ith stones of different 

 sizes, and resembling in its composition the boulder-clay or gla- 

 cial drift of Scotch geologists. It tells us of rocks ground down 

 by glaciers year after year in an arctic region — of the mud pro- 

 duced by such attrition being carried into the sea in the thawing- 

 season by overwhelming floods, " non sine montium clamore " 

 (see Dr. Kane's description of the great Humboldt glacier) — of 

 its dispersion over the sea-bed by the action of tides and cur- 

 rents — of the deposit thus formed being inhabited by a variety 

 of animals of a high northern type during a long and quiet 

 course of time — of the sea-bed being elevated by slow degrees 

 above the surface of the water by an agency which we cannot satis- 

 factorily explain, but which may be volcanic, or perhaps caused 

 by steam* — of the consequent extermination of these marine 

 animals — of an interval during which the raised sea-bed was 

 dry land — of a gradual amelioration of the climate — of another 

 oscillation of the earth's crust in a downward direction, when 

 the surface of the land, covered by its former deposit, again be- 

 came the bottom of the sea — and of a fresh succession of life, 

 which is still in existence. Thus a cycle of similar events con- 

 tinually recurs. Nothing is lost or altogether perishes; all the 

 old materials are used up, and assume new forms. It is the 

 fashion to quote Lucretius. I will only indulge in two lines ; 

 they seem not to be inapplicable to the present subject : — 



" Hue accedit uti quicque in sua corpora rursum 



dissoluat natura neque ad nilum interemat res." 



The kind assistance of Mr. Alder, Dr. Carpenter, the Rev. A. 

 M. Norman, Messrs. Henry and George Brady, Dr. M'Intosh, 

 and Mr. Peach — all of them experienced zoologists — enables me 

 to supplement this Report with notices of other departments of 

 the invertebrate fauna, which have resulted from the last grant 

 made to me. Several new species, especially among the smaller 

 Crustacea, have occurred ; and our knowledge of geographical 

 distribution has been not a little advanced by the work. Mr. 

 Norman's services especially deserve acknowledgment. 



I have made my usual contribution to the British Museum. 



* Vide Mr. R. A. Peacock's pamphlet ' Oa Steam as the Motive Power 

 in Earthquakes and Volcanoes, and on Cavities in the Earth's Crust.' 

 Jersey, 1866. 



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