in the Twenty Years before 1895 35 



as a fine infusorial earth. Later on, when passing through 

 the Arafura sea, lying to the westward of New Guinea, diatoms 

 were found in abundance, though the conditions, especially 

 those of temperature, were very different; but the salinity 

 of the tropical was nearly identical with that of the glacial 

 water. The density of both waters was low, the one on account 

 of the melting ice, and the other on account of the equatorial 

 rains. While carrying out operations in the Gulf of Guinea 

 on board the s.s. "Buccaneer," belonging to the Indiarubber, 

 Gutta Percha, and Telegraph Works Company of Silvertown, 

 I received abundant confirmation of the suitability of dilute 

 sea-water for supporting diatom life. Here, however, the 

 fresh river-water, which produces by mixture the almost 

 brackish sea-water, is accompanied by abundant land debris, 

 which prevents the formation of a pure diatom ocean ooze. 

 The deposits here have a predominant terrigenous character, 

 associated, however, with many siliceous organisms. 



Another pelagic deposit of a siliceous character is the 

 radiolarian ooze. Like the diatoms, the radiolarians are found 

 in water of low salinity, and in the Pacific, far from land, 

 they form true pelagic deposits. 



Starting, therefore, with expectation of finding a more 

 or less universal chalk formation at the bottom of the ocean, 

 the result of the "Challenger's" work in the first two years 

 was to open up a new geological world, and to show its 

 dependence on the physical conditions of the oceans. 



Ship and her Equipment. The "Challenger" was a 



decked corvette, and, when serving an ordinary commis- 



she carried twenty-one guns. These had been removed 



and the large ports enabled the ship to enjoy the most perfect 



1 ition. She was ship-rigged and her engines were able to 



li'-r ii knots at full speed. Her displacement was about 



2300 tons. Lik< all the men-of-war of her time she was built of 



wood, with very solid timbers. Her screw propeller could be 



ted up out of the water. This was a great convenience be- 



passagc was made under n! The whole amount 



of coal which she could < airy was very little more than that 



for manoeuvring the ship at the sounding and dredging 



3-2 



