1890-91.] Mr J. Y. Buchanan on Sulphur in Marine Muds. 21 
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.t 
A very remarkable 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 complete disappearance 
on drying. It is worthy of more particular mention. 
On 6th July 1879 the anchor dredge was put over in the Sound 
of Jura, where a depth of 120 fathoms was marked on the chart. It 
did not hold, and the yacht drifted, dragging it over the ground in 
a northerly direction before the wind and tide. Suddenly it 
hooked the ground, and brought the vessel up with a great strain 
on the cable. In heaving up it was with difficulty that the anchor 
was broken out of the ground ; and when it was brought to the 
surface the hag was full of a fine, unctuous, very tenacious blue 
clay, with some of the reddish-brown surface mud covering it. 
There were a few pieces of broken shell and rock, also smooth and 
rounded pebbles, which seemed to occur principally in the part 
separating the surface mud from the blue clay, but there was very 
little of this kind of matter. The whole bagful, weighing more than 
universal all along the African coast, and developed in a most remarkable manner 
on the coast flat within a considerable radius of the mouth of the river Congo. 
Here it was necessary to introduce a new designation for muds, and in this 
district 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 mice droppings, and they were covered 
with the same substance in 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 more especially in a depth of 50 fathoms, when the large ash 
bucket, to the use of which as a dredge I found it convenient to revert, came 
up full of these coprolites, without any flocculent matter whatever. All along 
the coast the mud of the locality was moulded in a similar way, though it was 
not so striking. When the course of the cruise took us across the open ocean to 
Ascension, and thence northwards, we were able to trace the transition of the more 
earthy shore coprolites into the more mineralised and glauconitic pelagic ones. 
