OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 685 



the Blue muds of terrigenous origin laid down in oceans free from the influence of ice, 

 under the term "glacial deposits," on account of: — 



(1) The absence or paucity of lime in the deposit. 



(2) The scarcity of organic constituents. 



(3) The very irregular size of the mineral components, especially the larger pieces. 



(4) The peculiar character of the " fine washings," chiefly rock flour. 



The lime poverty is probably due to a strong solvent action of the bottom water. 



The scarcity of diatoms, so numerous in the surface waters, is particularly striking, 

 and is probably to be accounted for by their being swept off northward by currents 

 which are set up by the melting of the sea ice. 



Distribution by icebergs is responsible for the irregular size of the mineral constitu- 

 ents of these deposits. 



Despite the irregular distribution of the mineral constituents, the glacial deposits 

 are, on the whole, the finer grained, the further they are from the Antarctic continent. 



In the Weddell Sea the glacial deposits are chiefly clays and muds, rarely sands. 

 Those most remote from the Antarctic continent are the most clayey and approach the 

 abyssal Red clays in some respects, but can always be difi'erentiated by the excess of 

 " rock flour " over true clay. 



The rock flour resulting from glacial abrasion, which constitutes the greater part of 

 the " fine washings," reaches its destination largely in suspension. 



Further information is required as to the sinking rates of rock flour and of diatoms, 

 and also as to the currents set up by the melting of sea ice within the pack-ice zone 

 to account for the comparatively sudden transition on the northern border of the 

 glacial deposits (in the Weddell Sea area) from diatom-free glacial clay to Diatom ooze 

 containing comparatively little rock flour. 



Chart of Deposits. 



This is based upon the information gathered by the Scotia, the map in the Challen- 

 ger volume on deep-sea deposits, Murray and Philippi's report on the deposits of the 

 Valdivia, and Schott's atlas (11). Some slight changes are made upon my chart 

 published in the Scot. Geog. Mag., 1905 — e.g. the deletion of the special area of " Blue 

 mud approximating to Red clay "—since, although the special characters of the glacial 

 deposit in this area are still insisted upon, it is now more clearly recognised that these 

 characters are due to the greater distance of this area from- the inland ice and that the 

 clay of this area is simply the finest grained type of glacial deposit. There are also 

 some alterations in the zone between S. Georgia and Buenos Ay res, consequent upon 

 the preliminary information received from Dr Heim of Lieut. Filchner's Expedition. 



TRANS. EOY. SOC. EDIN., VOL. XLIX., PART IIL (NO. 10). 91 



