INEQUALITIES OF SEDIMENTATION 347 



think, with tangles could get no specimen of the bottom whatever, and he 

 thinks he got sufficient evidence to prove the existence of a perfect swirl at 

 that depth ^ 



South of the Azores, Hjort found considerable tidal currents down 

 as deep as 800 metres.^ Reade^ has pointed out the evidence which 

 certain relatively deep soundings afford regarding the irregularity 

 of deposition. "In the Little Minch there is a 'deep' between the 

 Isle of Skye and North Uist with a sounding of 107 fathoms, 

 'rock' the surrounding bottom with soundings from 50 to 90 

 fathoms being shells, sand, or mud." 



Between the island of Rum and the island of Barra there are 

 a good many soundings showing rock, which are deeper than others 

 in the vicinity which have muddy bottoms. 



If we find hard ground we know that there must be something to prevent 

 the accumulation of sediment. Now the only thing that prevents the accumu- 

 lation of sediment is a current, and one help that telegraph soundings have 

 thus given to geographical science as an indication that tidal currents exist 

 even at very great depths in the open ocean.^ 



Most if not all deep-sea naturalists have noted even in the 

 deeper parts of the continental shelf evidences of current action. 

 Verrill has pointed out in the following quotation how such currents 

 over certain areas southeast of New England have prevented the 

 formation of argillaceous sediments. 



The prevalence of fine sand, along the Gulf-stream slope in this region, 

 and the remarkable absence of actual mud or clay deposits indicate that there 

 is here at the bottom, sufficient current to prevent for the most part the 

 deposition of fine argillaceous sediments over the upper portion of the slope, 

 in 65 to 150 fathoms. Such materials are probably carried along till they 

 eventually sink into the greater depths nearer the base of the slope or beyond, 

 in the ocean basin itself where the currents are less active. It is probable 



' Quoted by T. Mellard Reade, in "The North Atlantic as a Geological Basin," 

 Presidential Address, Liverpool Geol. Soc. Session, 1885-86. 



^ Johan Hjort, "The Michael Sars North Atlantic Deep-Sea Expedition 191 o," 

 Geog. Jour., XXXVII, 349-77. 



3 T. Mellard Reade, "Tidal Action as an Agent of Geological Change," 

 Philosophical Mag., XXV (1888), Series 5, p. 514, 



'' Ibid., p. 514. 



