SEA-FLOOR DEPOSITS. PART I 



307 



to be explained by the recorded 1 occurrence of igneous rocks such as gabbro and 

 diorite on the adjacent mainland. At the more northerly stations the mineral seems to 

 be less plentiful. Of the diatoms, Coscinodiscus, Thalassiosira and Fragilaria are the 

 genera most frequently seen ; Rhizosolenia, so abundant in samples from the Scotia Sea, 

 is relatively scarce. 



The sample from St. 136 differs from all the others in containing deep green glau- 

 conite among the abundant mineral grains. Some of this green material is also seen 

 infilling the central canal of sponge spicules. The finer constituent of the deposit con- 

 sists almost entirely of diatom frustules, along with some sponge spicules. The apparent 

 absence of calcareous material is noteworthy in view of the presence of glauconite, for 

 in other instances calcareous shelly material is constantly seen in association with this 

 mineral. 



The remaining three samples, from Sts. 28, 29 and 30 in West Cumberland Bay, are 

 classified as terrigenous mud. The material is exceedingly fine-grained, and recognizable 

 organic debris is restricted to occasional centric diatoms, though oil globules are com- 

 monly seen. The deposit, apart from the diatoms, is strikingly similar to sedimentary 

 material from the estuary of the River Mersey, and from the shores of the bay known 

 as the Wash, in England. 



THE SOUTH SHETL AND S (Plate XX) 

 This region is conveniently subdivided into two, (a) the Bransfield Strait, (b) the 

 Palmer Archipelago, represented by forty-two and fifteen samples respectively. The 

 stations are as follows: 



Table IV 



Two outlying stations (211, WS 400) to the north-west, also fall within the area of 

 the chart. 



0) Bransfield Strait, between the South Shetlands and the northern part of Graham 

 Land, has its greatest recorded depth (about 2000 m.) near its north-eastern outlet. 

 From this end of the strait, between King George Island and Trinity Peninsula, 



1 Tyrrell, G. W., 1930. The Petrography and Geology of South Georgia. Quest Report, pp. 28-34. 



