MARINE DEPOSITS OF PATAGONIA 201 



Burdwood Bank deposits is traced by the same author to the disintegrating rock, the 

 glauconite being of fossil and not of recent origin. An area similar to the Burdwood 

 Bank in this respect, lying in the south-west of the region considered, in which outcrops 

 of rock are being disintegrated by attrition and otherwise, would act as a reservoir from 

 which materials would be transported by currents and drifts to the north-east and 

 segregated into finer and finer grades the farther they travelled from their point of 

 origin. The glauconitic silts of the northern part of the region may therefore owe their 

 presence to some such combination of circumstances. 



No very large rivers discharge into the region under consideration, but the deposits 

 in the coastal belts are doubtless in large part derived from the land. In the Gulf of 

 San Jorge the deposits have been shown by Campbell Smith and Rayner (1934) to be 

 in part of volcanic origin. The deposits contain a high proportion of finely divided 

 volcanic glass and feldspar derived from the volcanoes of the Andes and, together with 

 the clay of non-volcanic origin, the materials are in process of forming a sedimentary 

 volcanic tuff. The white sands occurring off the Falkland Islands would appear to be of 

 terrigenous origin and to be derived from the quartzite rocks of the islands. * A deposit of 

 similar type north of the extremity of Tierra del Fuego may be of much the same origin, 

 while the deposits of like type on the north slope of the Burdwood Bank would indicate 

 an outcrop of quartzite rock there, similar to the outcrops of shales found on the bank 

 farther to the east by Macfadyen. 



SUMMARY 



This report describes the marine deposits of the Patagonian continental shelf from 

 the standpoint of providing data regarding the habitats of the bottom-living fauna of 

 the region. 



The topography of the sea-bottom of the region is described. Methods of separating 

 the deposits into their component grades of texture, and an improved form of levigator 

 for separating fine materials are described. The distribution of the various grades of 

 material in the deposits is given in detail. 



Twenty-nine types of deposit, falling into six groups, were found : their characters 

 and distribution are described. 



Finally the region is divided into grounds according to the texture of the deposits. 

 The distribution of the grounds, and the types of deposit found on them, are described. 



Though fuller data are required for a detailed discussion of the causes of the present 

 distribution of the deposits, the probable effect of the currents of the region in segre- 

 gating finer materials towards the north is pointed out. 



1 The quartzite rocks of the Devono-Carboniferous are shown by Baker (1924) to be characteristic of 

 West Falkland Island and the north part of East Falkland Island. 



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