SEA-FLOOR DEPOSITS. PART I 3 o 9 



which six samples are available. Three stations in the centre of the depression, namely 

 Sts. WS 395, WS 396 and WS 489, yield samples of diatomaceous mud at depths of 

 297, 318, and 308 m. respectively. On the southern slope of the depression (St. WS488) 

 terrigenous mud occurs at a depth of 220 m., while the samples from the northern slope 

 (Sts. WS 397 and WS 490) are sands from depths of 150 and 262 m. Incidentally, 

 another sandy deposit occurs at St. WS 399 at a depth of 738 m. on the submarine 

 extension of the South Shetland ridge. Farther east, between Deception Island and the 

 Palmer Archipelago (Sts. WS 494 A and WS 494 b) sands occur at depths of 1081 and 

 505 m. respectively. These stations are on either side of a channel between Deception 

 Island and Trinity Island, which connects with the open ocean to the north-west. Herdman 

 states that southward-flowing warm water enters this channel between Smith and Snow 

 Islands and passes south of Deception Island into the larger basin of Bransfield Strait. 

 The transport of detrital material by such a current would account for the accumulation 

 of sandy material in this area, especially if the existence of a ridge south of Deception 

 Island be substantiated. 



An outstanding feature of these deposits from the western part of the South Shetland 

 region is the occurrence of glaucophane among the detrital minerals. It is most abundant 

 in samples from Sts. WS 396 and WS 489, and it occurs in less quantity in samples from 

 Sts. WS 395 and WS 488 to the south, Sts. WS 494 a and WS 494 b to the east, and 

 Sts. WS 397, WS 490 and WS 399 to the north, while it has also been detected in a 

 sample from the Scotia Sea much farther north. The provenance of this mineral has yet 

 to be determined, but the size and distribution of the grains suggests that there may be 

 a current flowing eastward between Low Island and Brabant Island in addition to the 

 current already suggested by Herdman between Smith and Snow Islands. 



The diatomaceous muds of the South Shetlands region partake of the general cha- 

 racters described on p. 299. They are generally greenish muds with a considerable pro- 

 portion of flocculent material enclosing the detrital sand grains. The genera Coscino- 

 discus, Fragilaria and Cocconeis are most constantly present, as they occur in nearly every 

 sample examined. At some stations the predominance of these genera is rivalled by 

 Corethron and Rhizosolenia, which are especially well developed and abundant in the 

 sample from St. WS 384, for example. Other genera noted in many samples include 

 Tholassiosiro, Triceratium, Biddidphia and Thalassiothrix, and probably a critical ex- 

 amination of the diatom assemblages would reveal the presence of others. 



THE BELLINGSHAUSEN SEA (Plate XXI) 



This region is represented by samples from twenty-one stations. The most northerly 

 locality (St. WS 501), in Bismarck Strait south of Anvers Island, yields diatomaceous 

 mud at a depth of 583 m. The deposit is very similar to the diatomaceous mud which is 

 widely distributed in the Scotia Sea. In the shallower waters around the Biscoe Islands 

 (Sts. WS 498, WS 499) terrigenous material predominates, though diatom debris still 

 contributes largely to the bulk of the sediments. 



Farther to the south-west a series of eleven soundings taken along a north-west 



