MARINE DEPOSITS OF PATAGONIA 189 



(IX) SILT (Plate XII) 

 (Particles under ci mm. in diameter) 



Silt occurs in the bottom deposits everywhere in the region under investigation, but 

 over most of it is present in small amounts. South of lat. 46 30' S it forms up to 5 per 

 cent of the deposits of the continental shelf, but north of this latitude lies a wide belt 

 where it is present in larger amounts, as it is also on the eastward part of the continental 

 shelf north of the Falkland Islands. 



The Gulf of San Jorge contains a very high proportion of silt, 94 per cent, as does a 

 coastal strip off Point Gallegos with 89 per cent. East and north of the Gulf of San 

 Jorge there lies a wide area stretching as far east as long. 62 30' W which carries up to 

 45 per cent of silt. From the eastward edge of this area and extending in a southerly 

 direction to the edge of the continental shelf lies an area carrying up to 10 per cent of 

 silt. Towards the southern end of the latter area and stretching in from the continental 

 slope is a large patch carrying 17 per cent in its northern part and 83 per cent in its 

 southern part. North of the former area and eastwards on the continental slope the 

 proportion of silt in the deposits drops again to 3-5 per cent. 



North of the Falkland Islands an area bearing up to 33 per cent of silt extends up the 

 continental slope and on to the continental shelf as far west as long. 62 50' W. Towards 

 its north-west extremity the amount of silt in this area drops to 6 per cent, while on its 

 south-eastern border lies a patch in which the amount drops to 10 per cent. A belt 

 containing 12 per cent of silt runs in from this area towards the north coast of West 

 Falkland Island. 



In the bay of deep water north-west of the Burdwood Bank lies an area in which the 

 amount of silt in the deposits rises to 23 per cent, while on each side of the entrance of 

 the Strait of Magellan there is a patch containing silt up to 14 per cent in the northern 

 and up to 6 per cent in the southern one. 



Silt up to 13 per cent of the deposits occurs in a small patch to the north-west of the 

 area extending in westwards from the continental slope north of the Falkland Islands. 



Amounts higher than 5 per cent of silt in the deposits occur elsewhere only as a line 

 of patches extending north-west from the Jason Islands towards Point San Julian. 

 A coastal patch off the Jason Islands carries up to 25 per cent of the grade; farther to 

 the north-west two patches lie near the middle of the continental shelf and carry 6 and 

 7 per cent of silt respectively, while off Point San Julian a patch carries 6 per cent of silt 

 in the deposits. 



Consideration of the distribution of the deposits based on the texture of each sample 

 as a whole is deferred until a description of the types of deposit found in the region has 

 been given. 



TYPES OF DEPOSIT 



Dried samples from all the stations were assembled and arranged into twenty-nine 

 types, which fall into six well-defined groups. The groups are here designated by an 



