8 DISCOVERY REPORTS 



be put on this for classification, as volcanic minerals are quite common in the Blue Muds. Ninety- 

 five to ninety-eight per cent of the deposit consists of " fine washings ", but it is the character of these 

 that differentiates the deposit from the true Red Clays. There is certainly a considerably larger 

 proportion of true clay than in the typical Blue Muds, but there is still a large amount of very minute 

 land-derived mineral particles — the finest rock-flour — which has probably reached its destination 

 largely in suspension. This area is, on the whole, about 200 fathoms deeper than the surrounding seas, 

 but the difference in the character of the bottom is probably mainly accounted for by the comparative 

 infrequency of bergs within this area, owing to the set of the currents. Here the rate of accumulation 

 must be slower than in the Blue Mud area, but as not a single diatom was noted in any of the 

 samples, one is precluded from the hypothesis that these get lost amidst the glacial detritus. 



My own observations confirm most of the foregoing statements of Pirie, except that 

 I see httle difference between the two types of deposits beyond the much lesser pro- 

 portion of mineral particles in the "Blue Mud approximating to Red Clay" samples. 

 The foraminiferal fauna, as already mentioned, differs only in so fa»- as might be ex- 

 pected from a greater depth and distance from the Antarctic coast-line. All the Weddell 

 Sea soundings are very dissimilar in appearance and fauna from the Discovery deposits 

 obtained in the Bellingshausen and Scotia Seas, which were as a rule easily cleaned and 

 contained but a small percentage of clayey material. The Scotia material, on the other 

 hand, was so firm and coherent that many of the cores retained their form in the bottles 

 after thirty years in spirit, with the constant motion to which they have been subjected 

 at intervals. Practically none of the samples could be cleaned directly on a sieve, but 

 the material after slow drying generally broke down readily in hot water like a true clay, 

 and was then washed easily on a silk sieve of 150 meshes to the linear inch. In many 

 cases a second drying was necessary, and a few samples resisted even then, and were 

 finally broken down in hot soda solution. A fraction of the material passing through the 

 150-mesh sieve was washed on 200-mesh silk as a final test for the presence of Radiolaria 

 and diatoms. It was observed that when a sample had dried up in the bottle the layer 

 in contact with the glass was refractory, and could not be broken down. Presumably 

 some chemical reaction had been set up between the clay and the siUca of the glass. 



ABSENCE OF DIATOMS 



The most striking distinction between the Weddell Sea material and the Discovery 

 deposits from the Scotia and Bellingshausen Seas was the comparative absence of 

 diatoms. The Discovery deposits, which were mostly from comparatively shallow water, 

 contained diatoms in such abundance that they clogged the meshes of the sieves. In the 

 Weddell Sea deposits, on the other hand, the sight of a single diatom was a noteworthy 

 occurrence. Pirie refers to this in the foregoing extracts from his report, and elsewhere 

 he remarks: 



The relative amounts of diatoms in the surface waters and in the deposits form a marked contrast. 

 Over the whole of the Blue Mud area of the Weddell Sea diatoms are extremely abundant in the 

 surface waters; in the deposits on the other hand they are either entirely absent or present only in 

 very small quantity. Their maximum occurrence on the bottom is in about 51" or 52° S (St. 447, 

 A.E.) where, in the surface waters, they are comparatively infrequent. Can this absence in the Blue 

 Mud be accounted for by the rapid accumulation of the glacial detritus hiding them.' I think not — 



