20 THE DEPTH AND MARINE DEPOSITS OF THE PACIEIC OCEAN. 



percentage of calcium carbonate varies from to 20, per cent occurring 

 nine times, and the mean being 5.33 per cent. The mean percentage of 

 calcium carbonate in the Eed Clays of the whole ocean is, according to the 

 "Challenger" researches: 8.39 per cent in 18 samples from 2000 to 2500 

 fathoms, 7.16 per cent in 42 samples from 2500 to 3000 fathoms. The 

 depths are of the same order of magnitude, and yet the percentage for 

 the whole ocean is strikingly higher. The lower percentage in the case 

 of the " Albatross " Red Clay may very possibly be connected with the distri- 

 bution of the surface currents in this part of the ocean, and has certainly 

 nothing to do with depth, as many of the samples of Globigerina Ooze were 

 collected in depths not much less than those in which the Red Clay was 

 found, the average depth for Globigerina Ooze being 2001 fathoms against 

 2404 fathoms for Red Clay, and in a few cases Red Clay was found in 

 depths which at other stations allow Globigerina Ooze to be deposited. As 

 an illustration we may mention the Red Clay of Station 4544 (lat. 10° 38' N., 

 long. 106° 47' W.), where, although the depth is only 1955 fathoms, the 

 amount of calcium carbonate is equal to per cent. 



Diatom Ooze is represented by a most interesting sample which will be 

 found fully described later, and Radiolarian Ooze is represented by two un- 

 labelled samples ; Ptcropod Ooze is not represented in the collection. 



Terrigenous Deposits. Green Mud was found by the "Albatross" in two 

 localities, in 776 and 1036 fathoms, and Green Sand in 556 fathoms. The 

 calcium carbonate in one Green Mud was as high as 25 per cent ; in the 

 other only traces were found, while the percentage in the Green Sand was 5. 

 Glauconite is, of course, the characteristic mineral in these deposits, and 

 is usually accompanied by a green flocculent matter, to which Sir John 

 Murray and the late Professor Renard rightly attributed a vegetable origin. 

 To test the question two samples from the Agulhas Bank were placed in 

 small bottles and left to digest, the one in ether, the other in chloroform, 

 and in both cases the solvent took a pronounced green tinge, a fact which 

 strongly supports the above-mentioned view. 



Blue Mud was found off Callaoin 1490 and 1949 fathoms; in the former 

 there was no calcium carbonate, while the latter contained 5 per cent. 



Calcareous Mud. This name is applied here to a rather peculiar deposit 

 met with in lat. 21° 4' S., long. 133° 1' W., in 2225 fathoms. The re- 

 markable fact about this mud is that it is essentially composed of coccoliths 

 and Tunicate spicules, together witli a large quantity of calcium carbonate 



