MAEINE BIOLOGICAL STATION AT POET EEIN. 293 



are found lying scattered outside its base on the fine sand ; 

 but there is no deposit of smaller stones, gravel, and 

 resulting sand farther out, probably because in the wear- 

 ing of the rock and large detached blocks by the sea a 

 greai deal is removed in solution and the rest in suspension 

 as very fine mud — this we have found to be the case round 

 Puffin Island, which is also mountain hmestone. Bradda 

 Head, on the other hand, is a schistose metamorphic 

 Silurian rock, which breaks up into large fragments, and 

 these into smaller, and so forms deposits of dark slatey 

 more or less angular gravel, and then very coarse sand, 

 extending for some way out from the foot of the cliff. 



The influence of the shore rocks upon the httoral fauna 

 is an important subject upon which we have accumulated 

 some observations ; but the matter requires further work 

 and detailed discussion, and must be left over for a future 

 report. 



3. Probably the great bulk of the silicious sand which 

 forms so large a part of the floor of our sea is derived proxi- 

 mately — whatever may have been its ultimate source* — 

 from the great deposits of drift which were formed in the 

 neighbourhood during the Glacial period, and large tracts 

 of which may since have been broken up by the sea. 



4. As examples of a few pecuHar and specially note- 

 worthy deposits which are not simply "terrigenous" in 

 their origin, the following may be mentioned : — 



South-east of the Calf Sound, about two miles out, at a 

 depth of 20 fathoms, there is a white shelly sand which 

 seems to be almost wholly composed of animal remains. 

 There are broken fragments of the lamellibranchs Fecten, 

 Anomia, Pectunculus, Mactra, Venus, and Mijtilus, of the 

 gastropods CyprcEa, Buccinum, Emarginula^ Purpura, and 



* Probably to a gi-eat extent, Triassic sandstones. 



