MAEINE BIOLOGICAL STATION AT POET EEIN. 61 



in the Irish Sea, where the deposits ought all, from their 

 position, to be purely terrigenous, we meet with several 

 distinct varieties of sea-bottom which are not formed 

 mostly from the waste of the land, and do not contain 

 anything like 68 per cent, of silica ; but, on the contrary, 

 are formed very largely of the remains of bottom haunting 

 plants and animals, and may contain as little as 17 per 

 cent, of silica. Such are the nullipore bottoms, and the 

 shell sand and shell gravel met with in some places, and 

 the sand formed of comminuted spines and plates of 

 echinoids which we have found off the Calf Island. 

 These deposits are really much more nearly allied in their 

 nature, and in respect of the kind of rock which they 

 would probably form if consolidated,* to the calcareous 

 oozes amongst pelagic deposits, than they are to terri- 

 genous deposits, and yet they are formed on a continental 

 area close to land in shallow water. Moreover, although 

 agreeing with the pelagic deposits in being largely organic 

 in origin, they differ in being derived not from surface 

 organisms, but from plants (the nullipores) and animals 

 which lived on the bottom. Consequently the division of 

 deposits into "terrigenous" and "pelagic" ought to be 

 modified or replaced by the following classification : — - 



1. Terrigenous (Murray's term, restricted) — where the 



deposit is formed chiefly (say, at least 

 two-thirds, 66 %) of mineral particles 

 derived from the waste of the land. 



2. Neritic\ — where the deposit is largely of organic 



origin, its calcareous matter being 



* They seem closely comparable with the Coralline and Red Crag 

 formations of Suffolk. 



+ Adopted from Haeckel's term for the /one of shallow water marine 

 fauna, see "Plankton Stoidun" Jena, 1890; also Hickson'a "Fauna of 



Deep Sea," 1891. 



