34 ^ Retrospect of Oceanography 



found that the fresh animal caught with the tow-net contained 

 the mineral matter which would be required to account for the 

 red clay or for the argillaceous matter left on dissolving the lime 

 of a globigerina ooze. Hence that portion of Wyville Thomson's 

 ash theory, which ascribed an organic origin to the clay, had 

 to be abandoned. But mineral matter had been found to be 

 abundant all over the ocean-bed, and beyond certain limits 

 it could not be held to have been distributed by the agency 

 of ice. Hence it was necessary to call in some other agency, 

 if the mineral matter was to be taken from continents or islands. 

 It was to Mr Murray that the idea first suggested itself to 

 account for the mineral matter on the floor of the ocean by 

 the decomposition of pumice, which, after floating about 

 for a long time, had finally sunk at the spot. The eruption 

 of Krakatoa, and the fields of pumice which were met with 

 for many months afterwards floating all over the Indian 

 Ocean, and all of which in the end found its way to the bottom, 

 came as a welcome support to the theory ascribing a volcanic 

 origin to much of the mud found on all parts of the bottom 

 of the ocean. The microscopic analysis of the muds further 

 showed, by the abundance of glassy felspar and the absence 

 of quartz, that their parent rock was volcanic and not primary. 

 This happy idea of Mr Murray's, and the development which 

 it received in his hands, formed one of the greatest achieve- 

 ments of the expedition. 



In the Antarctic Ocean primary as well as igneous rocks 

 were found in the droppings of icebergs; and on more than 

 one occasion the trawl came up full of stones of all sizes, as 

 if it had been dragging over a moraine or a river-bed. On 

 such occasions there was a peculiar charm in going over them 

 with the hammer. It amounted in effect to a geological 

 excursion in the unknown regions of the Antarctic continent. 

 But the Antarctic Ocean afforded also a typical class of purely 

 pelagic deposit, the diatom ooze. Patches of deep olive- 

 green water were very common amongst the floating ice, 

 which itself was often stained by the same colour. This was 

 due to the chlorophyll of the minute diatoms. When they 

 died and sank to the bottom, their siliceous tests persisted 



