584 



Dr. W. B. Carpenter on the 



LJune 13, 



might not apply to various cases in which there is a like scantiness of 

 Animal remains in deposits of considerable thickness. — This view, how- 

 ever, has been called in question by Dr. M c Intosh ; who adduces, as 

 an objection to it, that many Annelids and Nemerteans abound in muddy 

 water, while some live nowhere else than amongst mud or muddy sand ; 

 and also that many littoral Sponges are found on extremely muddy 

 ground, while " the Siliceous Sponges all over the world affect a muddy 

 bottom." " In general," he adds, "muddy ground is found to be 

 " much more productive in marine life of all kinds, than where the 



" rocks, sea-weeds, and sands are pure Even where the margin 



" of the sea is rendered perfectly turbid from mud (and this, too, calca- 

 " reous), as at White-Cliff Bay, in the Isle of Wight, marine animals are 

 "abundant between tide-marks"*. None of the instances cited by Dr. 

 M c Intosh are really parallel to that of the abyssal deposit of the Mediter- 

 ranean ; for they are all cases of littoral deposit, consisting of particles very 

 much coarser (often mixed with sand), which the tidal movement of the 

 suspending water will keep washing-^, as much as washing-ow, the respi- 

 ratory surfaces. In no other part of our survey of the deep-sea bottom 

 has there been any difficulty in clearing the water immediately overlying it 

 by filtration. On our wonderfully rich " Holtenia-ground," the deposit in 

 which the Siliceous Sponges were imbedded was any thing but " muddy," 

 for it mainly consisted of Sand and Globigerinse ; and the water above it 

 was free from any turbidity, save that arising from the presence of very 

 young Globigerinse. The whitening of the littoral water produced by the 

 disintegration of Chalk-cliffs is not in the least degree comparable to the 

 turbidity which results from the presence of very finely divided particles of 

 clay ; for the Calcareous particles settle down comparatively quickly, and 

 are easily washed off again ; whilst the far more minute particles of Clay 

 are very long in subsiding, but, when they have been deposited, are ex- 

 tremely adhesive. 



75. My own dredging-experience certainly does not bear out Dr. 

 Mcintosh's statement as to the more productive character of muddy 

 bottoms. Those who have worked at Tenby or in Lamlash Bay will be 

 slow to admit that "purity" of the "rocks, sea-weeds, and sands" in 

 those localities is less favourable to Marine Life than the foulness of " odo- 

 riferous mud though there are doubtless animals to which the latter is 

 congenial. — The following passage from Dana's recent Treatise " On Corals 

 and Coral Islands " gives the experience of a very accomplished observer, 

 acquired over a very extensive range. " The effects of sediment on grow- 

 " ing Zoophytes are strongly marked, and may often be perceived when a 

 " mingling of fresh water alone produces little influence. We have men- 

 " tioned that the Pontes are reduced to flattened masses by the lodgment of 

 " sediment. The same takes place with the hemispheres of Astrcea ; and it 

 " is not uncommon that in this way large areas at top are deprived of life. 

 * Annals of Nat. Hist., Jan. 1872, pp. 10-13. 



