OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. G75 



ing (7) ; although this was south of 70° S. lat., it is possibly a widespread condition. 



Further evidence of their presence is afforded by the movements of icebergs, the deeply 



immersed portions of which are influenced by this current, carrying them northward 



despite the absence of prevalent winds from the south. The diatom skeletons, being 



light, are carried off" by this current and only sink to the bottom farther north, where, 



presumably, the current is dissipated. The heavier glacial material, carried chiefly in 



the base of the bergs (ground morainic matter) — which parts melt early — sinks easily 



and is deposited nearer the Antarctic land. Much of the finest rock flour, however, is 



carried, perhaps partly within the ice of the bergs, but largely in suspension, to a very 



considerable distance from Antarctic land into the S. Atlantic. Whilst this theory 



provides a working hypothesis to account for the peculiar distribution of diatoms, it 



seems to me not quite satisfying in its failure to account completely for the rapid 



transition from glacial clay composed largely of rock flour and containing no diatoms 



to a diatom ooze with almost no clay or rock flour. The distribution of the glacial 



clay and Diatom ooze and the limits within which pack-ice occurs — so far as we know these 



two sets of facts (8) — also do not seem to correspond sufficiently closely to be explained 



fully by this theory. The Gauss and Valdivia reports read almost as if the margin 



of the glacial deposits corresponded exactly with the pack-ice zone, the coarser glacial 



detritus sinking mainly within the inner portion of the pack-ice zone, the diatoms and 



fine rock flour being carried northwards by the current set up by the melting surface 



ice, to sink outside the pack-ice area. In a general way this is probably true. Where 



pack-ice is known to come far north — as, for instance, in the eastern part of the 



S. Atlantic — the Diatom ooze area also extends further northwards, but there ought also 



by rights to be a considerable admixture of fine rock flour in the ooze, which does not 



appear to be the case. Observations on the rates of sinking of diatom frustules and 



rock flour would throw further light on this interesting point, and further data on the 



distribution of ice and of the circum polar glacial clay and Diatom ooze are required 



before a completely satisfactory explanation is forthcoming. (See also under " Glacial 



Muds and Clays," p. 677 et seq.) 



Diatoms in Deposits. 



A selected series of deposits containing diatoms was sent to Professor H. H. Gran 

 of Christiania, who kindly off"ered to examine and report upon them. The selection 

 included not merely those deposits classified as Diatom oozes, but also a few specimens of 

 glacial clays in which I had noted the presence of diatoms in my examination, and of 

 shallow-water deposits from the coast and neighbourhood of the S. Orkneys. It is 

 convenient to include them all at this point. The following is Professor Gran's 

 preliminary report on the samples, which he has been good enough to allow me to make 

 use of pending his complete identification and description. 



" The samples are of two different types — 



"(1) Deep-sea deposits of a very uniform character [as regards their diatoms 



