22 Proceedings of Royal Society of Edinburgh. [sess. 
1 cwt., consisted almost entirely of homogeneous blue clay of a 
tenacity similar to the clay dug for brickmaking, and quite different 
from ordinary “ blue muds.” The clay was rather foul-smelling, and 
gave off abundance of sulphuretted hydrogen when treated with 
hydrochloric acid. It was so tenacious that it was impossible to 
break it up in water for the purpose of levigation, which is always 
very easily accomplished with ordinary muds. A considerable por- 
tion of it was dried and taken for analysis. It was found that, as soon 
as dry, not a trace of sulphide was to be found ; hut the mass of the 
clay was permeated with fine particles of oxide of iron, each of which 
represented a previous particle of sulphide. A specimen of this clay 
is on the table. The contrast between the fresh moist clay, which 
was thoroughly impregnated with sulphides, and the dried clay, 
without a trace of them, was very striking.* 
The fact then had been demonstrated that the mud is being con- 
tinually passed and repassed through the bodies of animals in- 
habiting the bottom of the sea. In doing so the mineral matter of 
which it consists comes in contact with the organic secretions of the 
animals, mixed with sea water, and is ground up along with them in 
the milling organs of the animals. 
The Eeducing Action of organic matter on sulphates has long been 
known, and its importance as an agent in geological metamorphosis 
was thoroughly recognised by Bischof.f 
The effect of Trituration in promoting the chemical decomposition 
of silicates by water was demonstrated by Daubree,}; more par- 
ticularly in the case of Felspar. I found the observations to hold 
good also for Augite. Clear crystals of this mineral from the 
Tristan da Cunha group, when pulverised with water in an agate 
mortar, rendered the water alkaline to turmeric paper. 
It is evident therefore that at the bottom of the sea a number of 
conditions occur together, which are favourable to the production 
of chemical change. The ground animals, in the search of food, 
pass the mud through their bodies, grinding it up, and bringing it 
* A condensed account of my views of the part played by the sulphates of 
the sea water in the production of the ochreous deposits on the bottom of the 
ocean, and of the carbonate of lime of the shells of the Mollusca, is published 
in the Reports of the British Association (York), 1881, p. 584. 
t Bischof, Lehrluch der Chemischen und Physikalischen GeoJogie (1868), i. 
31, 358. X Daubree, Geologic Experimentale , i. 268. 
