& 



334 REPORT — 1894. 



organic growth. The stones evidently have not been transported far by 

 water, or they would be well rounded, like the pebbles found in our 

 Eocene lieds. The encrusting organisms show also that the fragments 

 have lain undisturbed on the sea-bed, yet they have often been derived 

 from far-distant sources. Though no Glacial strise were observed, and no 

 undoubted sub-fossil arctic shells have yet been found at these localities, 

 yet there seems little doubt that the bulk of the material on the sea- 

 bottom over this area has been derived from the breaking up of pre- 

 existing Glacial deposits. This may occur at a depth of several fathoms 

 through the gradual washing away of the muddy and sandy matrix of a 

 boulder clay or Glacial gravel. Coarse gravel is thus caused to accu- 

 mulate at a spot where the currents may be too feeble to transport 

 anything but sand. 



' This sulimarine origin of angular gravel deposits should not be for- 

 gotten, for it affects the lithological character of the sea-bottom over 

 most of the area which was formerly glaciated, even as far south as 

 Cornwall. On the other hand, it does not affect, except to a small 

 extent, the sea-bed beyond the former limit of the ice, and it does not 

 affect pre-Glacial deposits. Thus we must always expect to find at 

 similar depths the same fauna associated with deposits of finer texture 

 as soon as we leave the glaciated area, or when we go back into Tertiary 

 times. 



' It is also worth noting that the occurrence of a stony bottom at 

 twenty or thirty fathoms — where normally there Avould be no deposit 

 coarser than sand — will probably lead to a disproportionate increase of 

 all encrusting organisms, and of all organisms needing a solid base. TJiis 

 lias certainly taken place, as anyone studying our shoal-water Tertiary 

 deposits will have observed. They contain few stones, and though each 

 stone or dead shell may be covered with encrusting organisms, yet the 

 relative proportion of these to the free forms is far smaller than seems 

 commonly to be the case in the seas that now wash our shores. The 

 sole exception to this rule among the British Tertiary strata is found in 

 the Coralline Crag, in which the contemporaneous consolidation of the 

 limestone was sufficient to provide the necessary solid base for tlio 

 encrusting and fixed organisms so abundant in that deposit.' 



In conclusion, it is clear that this investigation of oar modern sul)- 

 marine deposits, their distribution, nature, origin, and associated fauna, 

 has geological applications, and that our results may be of some importance 

 to palaeontologists in determining the conditions under which the faun;i 

 of a particular horizon existed in the past ; but, from our point of view, 

 the matter is a purely Biological one. We consider it of primary impor- 

 tance, in studying the distribution of the marine animals in our district, to 

 investigate as minutely as possible their environment, and that not merely 

 because it gives us some of the factors and possibly the explanation of the 

 distribution, but also on account of the light it may throw upon the 

 habits, variations, and other important characteristics of the species. 



The Committee apply to be reappointed, with a small grant to 

 defray part of the expenses of the dredging expeditions. 



