3 o6 DISCOVERY REPORTS 



Bank belongs to the shallow seas of the continental shelf. It may be noted that frag- 

 ments of shale from St. WS 87 have been examined and described by W. A. Macfayden, 1 

 who deduces a Cretaceous age for the shale from the evidence of Foraminifera contained 

 therein. He also suggests, from the abundance of shale pebbles in the dredgings, that 

 the beds must outcrop on the sea-bottom at or close to the stations. Some of the shale 

 fragments are highly glauconitic, grains of this mineral being prominently exposed on 

 the worn surfaces. It follows that some (at least) of the glauconite grains present in the 

 modern deposit are "derived" by disintegration of the shale. 



Two stations (228 and 230) are situated in the depression between the Falkland 

 Islands and Burdwood Bank, where depths of 660 and 675 m. are recorded. The first- 

 named station yields a diatomaceous mud which is similar in general constitution to the 

 great majority of such deposits from the Scotia Sea. The deposit from St. 230 is classed 

 as terrigenous mud because of the abundance of detrital mineral grains and the absence 

 of recognizable organic remains. This procedure, though unavoidable, is somewhat 

 unsatisfactory, for it leaves out of account the considerable proportion of flocculent 

 material which contributes largely to the bulk of the deposit. It is undoubtedly of 

 organic origin but is so indefinite that its precise nature cannot be determined. But 

 from the geological standpoint the omission is not so serious ; for when thoroughly dried, 

 the flocculent material shrinks to a mere film round the detrital grains, and the deposit 

 eventually approaches the type exemplified by the marine silts of the English Fenland. 



SOUTH GEORGIA (Plate XIX) 



From this region the 'Discovery' collected twenty-three samples, while a further 

 twenty-one were obtained by the 'William Scoresby'. The majority of the forty-five 

 samples are of very uniform character, falling within the group classified in this report 

 as diatomaceous mud. 



Judging by the records of soundings, South Georgia is surrounded by a belt of shallow 

 sea, varying from 20 to 300 m. in depth. Outside this area, usually at about 30 or 40 

 miles from the island, the depth increases rapidly to 1000 m. and more. This variation 

 in depth appears to have little (if any) influence on the character of the deposits, for 

 diatomaceous mud from Sts. 129 (depth 1001 m.), 151 (depth 3200 m.), WS 26 (depth 

 1 180 m.) and WS 63 (depth 1752 m.), are essentially similar to diatomaceous mud from 

 stations close inshore. The finer fraction consists mainly of diatoms, with sponge 

 spicules and Radiolaria in subordinate quantity. Mineral grains are present in con- 

 spicuous proportion, and the size of the grains appears not to be related to depth alone. 

 For, at St. 129 the largest grains noted are about o-i mm. across, whereas at St. 151 

 grains reaching 0-2 mm. in diameter were noted, though the depth is three times that 

 of the former locality. Green hornblende occurs in several of the samples, particularly 

 those from the more southerly stations. The relative abundance of this mineral in 

 deposits from the mouth of Drygalski Fjord, at the south-east of the island, is probably 



1 Macfayden, W. S., 1933. Fossil Foraminifera from the Burdwood Bank and their geological significance. 

 Discovery Reports, vn, pp. 1-16. 



