684 DR J. H. HARVEY PIRIE ON DEEP-SEA DEPOSITS 



include very minute fragments of minerals. There is, however, a sufficiency of clayey 

 material in practically all the glacial deposits of the Weddell Sea, and more so in some 

 than in others, to give them the gross character of a clay ; and, as already mentioned, 

 their microscopic constitution is indistinguishable from the clay of the Portobello brick- 

 field, a shallow-water glacial deposit. This character also serves to differentiate them 

 from most Blue muds or terrigenous deposits laid down uninfluenced by the action of ice, 

 some of which may be described as clays, but the majority are rather earthy than clayey 

 in character. 



The clayey nature, both microscopically and in its gross characteristics, is distinctly 

 more pronounced in the deposits from the deeper and more northerly portions of ths 

 Weddell Sea furthest from the Antarctic inland ice. The colour of these tends to be 

 of a brown shade of grey rather than the more common green or blue-grey of the others ; 

 they are more unctuous to the touch, very tenacious, and require more rubbing to break 

 them down for microscopic examination. Their mineral particles amount only to from 

 2 to 5 per cent., whilst their fine washings constitute from 95 to 98 per cent, of the 

 whole deposit, and of this a greater amount than elsewhere consists of amorphous clayey 

 material, although even here that plays a much smaller role quantitatively than "rock 

 flour." The different character of this group is so marked that in my preliminary 

 account of these deposits 1 distinguished this area as one of " Blue mud approximating 

 to Red clay in some of its characters." The points in which they resemble Red clays 

 are (l) tough clayey character; (2) brownish colour ; (3) paucity of mineral particles, 

 those present consisting more largely of volcanic minerals ; (4) occasional presence of 

 palagonite ; (5) absence of lime. I would not now, however, press this resemblance, 

 although having drawn attention to it has served to emphasise the change in type of 

 the glacial deposits with increasing distance from the land whence their constituent 

 parts are drawn. The points of difference from a true abyssal Red clay are obvious 

 enough, more particularly — as I quite recognised and pointed out at the same time — the 

 character of the fine washings. These are not predominatingly clay as in the Red clays, 

 but land-derived mineral particles, the finest rock flour resulting from the grinding and 

 abrading action of the Antarctic ice-sheets and glaciers. 



This rock flour from the ground moraine of the Antarctic ice-sheets is probably 

 liberated largely within a comparatively short distance of the land, although a certain 

 amount embedded more deeply in the lowest portion of the bergs is doubtlessly only 

 set free further north as melting of the berg ice proceeds. Suspended in the water, it 

 is carried for great distances before it settles down ; but naturally the finest particles 

 remain in suspension longest, and it is therefore only these that are found in the area 

 furthest from Antarctica, although rocks and some mineral particles are to be expected 

 as the result of immediate deposition by the setting free of deeper contained debris as 

 the bergs are melting in lower latitudes. Sea-ice plays very little part in the dis- 

 tribution of the material making up these glacial deposits. 



To sum up, the terrigenous deposits of the Weddell Sea may be distinguished from 



