Marine Muds and Nodules 137 



been produced out of the silicates of the mud by the ground 

 animals forming sulphide of calcium, which was transformed 

 into carbonate by the carbonic acid of the water. On the 

 following day another haul was got in the same locality and 

 with similar results; it is noted that "Sticking to the outside 

 of the bag were many legs of ophiurids, which will account 

 for the coprolites." When attention had once been paid 

 to it, the coprolitic moulding of the mud, when of a suitable 

 consistency, was found to be practically universal round our 



s 1 . 



Shore muds, that is, the terrigenous deposits which are 

 found all along the shores of continents, and even at great 

 depths generally present the characteristic appearance of a 

 reddish surface layer, overlying a bluish substratum. This 

 characteristic is observed in deposits even far out at sea, 

 and, where it is not masked by large amounts of calcareous 

 matter, is evidently due to the oxidation of the bluish ferrous 

 salts, on their coming in contact with the sea-water, which 

 always contains dissolved oxygen. 



larkable example of a blue clay for it was 

 too tenacious to be called a mud was obtained in the Sound 

 of Jura, and it was particularly noticeable for the amount 

 of sulphides which it contained, and instructive by their 



1 Later, in the year 1886, when accompanying the expedition to survey 

 the < . ;nea in the steamship "Buccaneer," I found the same thing 



practically universal all along the African coast, and developed in a most 

 remarkable manner on the coast flat within a considerable radius of th< 

 mouth of the river Congo. Here it was necessary to introduce a new 

 desir muds, and in t the most frequent entries in the 



deck-book as to the nature of the bottom are " cop. m . " meaning coprolitic 

 mud. These so-called coprolites were almost jet black and of the size of 



droppings, and they were covered with the same substan. 

 flocculent form, or were free from it, according to the scour of the tide in 

 the locality. It was best developed in comparatively shallow water, and 



especially in a depth of 50 fathoms, v Urge ash buck' 



;se of which as a dredge I found it . nvcnient to revert, came up full 



rse coprolites, without any floco tcr whate .tlong 



the coast the mud of the locality was moulded in a similar way, though it 

 was not so striking >c course of the cruise took us across the open 



ocean to Ascension, and thence northwards, we were able to tra< 

 transition of the more earthy shore coprolites into the more mineralised 

 an.! Kl.uio.iiitir j>rl.ii;ir DOM 



