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DISCOVERY REPORTS 



DISTRIBUTION OF THE GRADES 



The results obtained from the quantitative analysis are tabulated and charted to show 

 the distribution of the various grades of material present in the deposits. Each grade is 

 first considered separately and charted according to the percentage in which it is 

 present. Contours are then drawn round areas of similar percentages, thus defining the 

 grounds covered by each grade. Thereafter the texture of each bottom sample as a 

 whole is charted by means of an index number obtained from the proportions of the 

 various grades present in each sample. The grounds covered by deposits of similar 

 texture are defined by contours. 



(I) LARGE FRAGMENTS (Plate IV) 

 (Material 15 mm. in diameter and over) 



Most of the region under consideration is free from large fragments, which occur 

 mainly in isolated patches and not in extensive grounds. In the Gulf of San Jorge a 

 greenish grey Tuff (Campbell Smith, W., and Rayner, G., 1934) was picked up in some 

 quantity by the trawl, while off the coast to the south of Cape Tres Puntas and Point 

 Deseado lies a ground in which large fragments are present in quantity varying from 

 5 to 59 per cent of the deposits. Farther to the east lies a smaller area with 8-10 per cent 

 of large fragments. In lat. 45 13' S and long. 59 56' 30" W a patch containing 7 per 

 cent of large fragments lies on the edge of deep water. 



Off the southern shores of the Falkland Islands large fragments form up to 48 per cent 

 of the deposits in the shallower water, but the proportion rapidly falls off to 12-15 per 

 cent between the depths of 200 and 300 m., and the grade is absent below 300 m. The 

 stations on the Burdwood Bank show up to 55 per cent of large fragments on the shal- 

 lower part with the percentage falling to 1 5 per cent by 200 m. and absent below. The 

 occurrence of outcrops of rock on the Burdwood Bank is regarded by Macfadyen (1933) 

 as probable, from the occurrence of loose fossil Foraminifera in the deposits. 



Between the Falkland Islands and the entrance of the Strait of Magellan lies an ex- 

 tensive patch carrying 35-51 per cent of large fragments, while another smaller one lies 

 off the coast of Tierra del Fuego to the south of the entrance to the Strait. 



On the line joining the Jason Islands to the south end of the large-fragment grounds 

 south of Point Deseado lie two areas of large fragments. The larger and easternmost 

 one, containing 16-60 per cent of large fragments, lies in the middle of the continental 

 shelf between lat. 50 and 51 S; while the smaller and more westerly one, carrying 

 1-6 per cent of large fragments, lies between lat. 49 40' and 50 S, to the south of the 

 Point Deseado ground. 



The remainder of the stations from which large fragments were obtained are few in 

 number and widely scattered over the continental shelf south of lat. 50 S. At St. WS 

 783 in lat. 50 02' 45" S and long. 6o° 10' W, the sample obtained shows only 1 per cent 

 of large fragments, but two unsuccessful hauls were made at this station before the 

 sample was obtained. In the first two hauls the dredge was bent by rock. This may 



