280 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



present not clear. The red clay is entirely mineral in character, 

 consisting of particles of 2 microns (.002 mm) diameter, together with 

 finer clay material. It has been regarded as in part the insoluble resi- 

 due of the skeletons of organisms, left after solution of calcium car- 

 bonate, silica, and other constituents by subsidence through the 

 great depths. But its mineral constitution does not lend support 

 to this view, nor is it borne out by the characters of the insoluble 

 residues shown by chemical analyses of skeletons of marine animals. 

 More probably it results from the slow accumulation of fine volcanic 

 dust, which is blown over the ocean for great distances, and from 

 the decomposition of volcanic products such as ash, pumice, and 

 basalt, which have fallen into ocean waters. In addition, however, 

 to minerals such as felspar and augite (and in the clayey portion 

 montmorillonite) which could be derived in this way, there are many 

 tiny grains of quartz, a mineral unlikely to occur except rarely in 

 products of oceanic volcanoes. The presence of these makes it 

 seem likely that wind-blown material other than volcanic dust must 

 reach the depths. Indeed, Stefansson observed that off-shore winds 

 carried sand and even gravel far out on to off-shore ice, and others 

 have recorded dust-falls derived from the Saharan region, at a distance 

 of 1,700 miles west of the African coast. In the great 1912 eruption 

 of Katmai in Alaska, a thickness of 6 mm of volcanic dust was de- 

 posited at 220 miles distance; also, the effects of dust from Krakatoa 

 carried three times round the earth in 1883 are still remembered. 

 Further, it has been observed that in samples from both the Narrow 

 Seas and the South Atlantic relatively coarse grains of quartz are 

 buoyed up by filamentous masses of flocculent protoplasmic or other 

 organic material and can travel thus for long distances in the sea. 



Little work has been done on the constitution of the clayey fractions 

 of pelagic deposits, but preliminary X-ray investigations by Prof. 

 C. W. Correns of Rostock showed that a sample of red clay collected 

 by the Meteor is composed of kaolinite, calcite, and muscovite mica. 

 There is here an extensive field for investigation. 



When we recall how these pelagic deposits have arisen, we realize 

 that the rate of accumulation must be extremely slow. Schott 

 has estimated that in 1,000 years a thickness of 17.8 mm of blue 

 mud, 12 mm of globigerina ooze, and less than 8.6 mm of red clay 

 would be laid down. No surprise need be felt, therefore, at the 

 oft-quoted statement that teeth of sharks dredged from the ocean 

 floor, of species now extinct, have been found to be covered with 

 only a film of deposit. On the other hand, there is the surpris- 

 ing record of some inch or two of globigerina ooze found cover- 

 ing the Atlantic cable when it was brought to the surface for repair. 

 An inch of deposit in less than a century is almost incredible; and 



