Marine Muds and Nodules 147 



in Loch Oich. It is chemically quite distinct from the marine 

 clays, being much more acid. The amount of matter extracted 

 by chloroform is enormous, being 374 milligrms. per loogrms., 

 most of which is oil or wax, but containing 4 milligrms. of 

 oxidisable sulphur. It is not impossible that in this case 

 the sulphur may exist as an organic compound; and the 

 amount of oily matter in the clay is interesting in the indication 

 which it gives of the possible mode of formation of our oil 

 bearing shales. 



26 is from the anchorage of Isle Oronsay in the Sound 

 of Sleat. 



No. 27 is from a depth of 87 fathoms off Garroch Head, 

 in the Firth of Clyde. Both in this case and in that of No. 26 

 the amounts of residue and of sulphur are insignificant. 



Sulphur was thus detected in all these samples and deter- 

 mined in the greater number of them. Putting aside shallow 

 water coast muds, the largest amounts of sulphur are found 

 in the Celebes Sea (No. 16), in the diatomaceous ooze of the 

 Antarctic (No. 18), and in the radiolarian ooze of the Pacific 

 20). So far, therefore, as it goes, we have the evidence 

 of the sulphur in favour of former organic agency. It is 

 hy of remark that the property of giving off alkaline 

 r on heating has in the course of years disappeared, and 

 in its place the nodules on being heated give off acid vapours, 

 i. ii i- true, contain some ammonia, but along with an 

 excess of nitric acid, which is without doubt due to the gradual 

 ition of the nitrogenous matter. It is possible that the 

 . divided sulphur may diminish and finally disappear in tin 

 same way. But in 1881, there was still enough to be easily d< 

 mined. Let us consider the chemical reactions more closely. 



When a mud containing ferrous sulphide i^ tre.ited with 



dilute hydrochloric acid, the sulphide dissolve with evolution 



ilplmretted hydrogen, so long as there is no substr 



nt whieh has a decomposing action on the sulphuretted 



gen, If there be ferric salt either mixed with the mud 



-1 ut i>n. th-n it i- reduced to ferrous salt, with the 



e.|uiv.ilent amount of H t S and separation 



:lphur. If th- in ii. -.ilt !>< m excess, no sulphuretted 



102 



