172 On the Composition of Oceanic 



Packed as closely as possible in a graduated cylinder of 37 

 millimetres internal diameter, they occupied a length of 130 

 millimetres, reaching to 146 c.c. on the graduation. I then 

 poured in 100 c.c. water, which stood at 158 c.c. Hence the 

 volume of the nodules was 58 c.c., and the average volume of 

 one was 0-7 c.c., and their density 2-46. The shells were all 

 dead, and principally Pecten ; they weighed 35 grammes. The 

 following was the mechanical composition of the mud: 



Nodules . . . . 142-7 grammes 30 per cent. 



Shells 35 7i 



Sandy clay . . 289 62$ 



Total . . . . 466-7 ,, 100 ,, 



Of twenty-two nodules which were split open, sixteen con- 

 tained soft nuclei of about the size of a pea, and apparently 

 very rich in manganese. One of these nuclei was so slightly 

 attached to the rind as to fall out when the nodule was split. 

 The rind is always very hard and gritty, and when the oxides 

 of iron and manganese are removed by hydrochloric acid, it 

 falls into a mass of sand, similar to that which makes up a 

 large proportion of the rind. This agrees with the idea that 

 the nodules are agglomerations of the mud found in situ, and 

 cemented by the ochreous oxides. One nodule (No. 24) was 

 interesting, as showing the complete soft kernel, loose, in a 

 cavity of mud, the rind not having as yet formed, although it 

 was evidently forming, the mud being stained from the inner 

 wall of the shell outwards. No. 25 was a similar nodule, only 

 the kernel had no free space round it. The mud round it was 

 stained yellow. This seems to be very general with the growing 

 nodule; the oxide of iron spreads itself in front of the oxide 

 of manganese. A little of the yellow shell gives no manganese 

 reaction with hydrochloric acid. A nodule of the size of a 

 pea was found, resembling the others perfectly, except that it 

 contained Fe 2 O 3 , and no MnO 2 . Very careful examination of 

 the mud from which the nodules and shells had been removed 

 showed that perfect nodules exist down to the size of a pin-head, 

 and all through the mud there were specks showing where 

 probably nodules had begun to form. Although so near the 

 shore, the mud contains hardly any pebbles larger than a 



