342 DISCOVERY REPORTS 



Tides. Between May and October 1903, tidal observations were carried out from the 

 ' Scotia ' as she lay frozen in in Scotia Bay. According to G. H. Darwin/ who examined 

 the data thus collected, the tides of the South Orkneys seem to be normal for a place in 

 the Southern Ocean. The semi-diurnal tides are considerable, but the solar tide is un- 

 usually large compared with the lunar tide. The semi-diurnal tides are almost exactly 

 "inverted", so that low water occurs very nearly when the moon is on the meridian. 



From the somewhat cursory observations made in January 1933, the rise and fall does 

 not appear to be very great, at any rate not so great that correction need be applied to 

 soundings of six fathoms or over. Powell records a rise of about six to eight feet in the 

 Sandefjord Bay district and a slightly greater rise and fall, about ten feet, at Spence 

 Harbour, adding that in the latter locality "the tides do not ebb and flow regularly: it 

 sometimes remains low water for the whole day, at other times it keeps up for the same 

 space of time". Through the straits and narrow channels the tides run strongly. Powell 

 experienced a current of about three and a half knots in Lewthwaite and Washington 

 Straits, while at Sandefjord Bay, in the narrow passage between Spine Island and the 

 mainland, he records a flood tide of about four knots. The 'Discovery 11' encountered 

 a very strong tidal stream in the Narrows adjoining. Small bergs are generally carried 

 on the tide and are often to be found streaming through Lewthwaite and Washington 

 Straits with the current. They are inclined to hamper navigation in narrow waters. 

 Tide rips are exceedingly cornmon in the straits and in a lesser degree around the coasts 

 in general. They are most noticeable when the weather is calm. 



THE SCOTIA ARC2 



The recent investigations of Herdman on the bottom relief of the Scotia Sea have 

 established beyond doubt that a rise or submarine ridge extends eastwards from Tierra 

 del Fuego through Staten Island, the Burdwood Bank, the Shag Rocks, South Georgia 

 and the Gierke Rocks, to the volcanic arc of the South Sandwich Islands, and thence, 

 sweeping round to the westward through the South Orkneys, eventually links up with 

 Graham Land and the South Shetland Archipelago. In other words, if we accept the 

 views of most geologists, the South Orkneys, together with the South Sandwich Islands, 

 South Georgia and the rest, may be regarded as the unsubmerged remnants of a great 

 eastwardly directed mountain loop which once connected the southern tip of the Andes 

 with the mountains of Graham Land : for it has been shown that the latter are in many 

 respects geologically identical with their Patagonian neighbours. Although the idea of a 

 tectonic connection between Graham Land and Patagonia was of much earlier origin, 



1 Scientific results of the 'Scotia' 1902-4, 11, p. 323. 



2 Recent and fuller accounts of the Scotia Arc problem and its history, to which the author is indebted, 

 will be found in the Discovery Reports: Kemp, S., and Nelson, A. L., 193 1, The South Sandivich Islands, 

 with a Report on Rock Specimens by G. W. Tyrrell, ill, pp. 148, 154-5, 191-7; Herdman, H. F. P., 1932, 

 Report on Soundings taken during the Discovery Investigations, 1926-32, vi, pp. 214-29, plate XLV; Mac- 

 fadyen, W. A., 1933, Fossil Foraminifera from the Burdwood Bank and their Geological Significance, Vii, 

 pp. 13-15 ; see also G. W. Tyrrell in Report on the Geological Collections made during the Voyage of the ' Quest ', 

 British Museum (Natural History), 1930, pp. 51-4. 



