of Edinburgh, Sessio7i 1883-84. 
515 
mask the character of the clayey matter in which they are em- 
bedded. The mineral particles are seldom larger than O'Ol mni. 
in diameter, but descend from this size to the merest points. It is im- 
possible, on account of their minuteness, to say to what mineral species 
they belong, their optical reactions are insensible, their outlines too 
irregular, and all special coloration has disappeared. All that can 
be reasonably said is that these minute mineral particles probably 
belong to the same species as the larger particles in the same deposit, 
such as felspar, hornblende, magnetite, &c. In the case of pumice 
and siliceous organisms the fragments can, owing to their structure, 
be recognised when of a much less size than in the case of the above 
minerals. 
It can be made out by means of the microscope that the colouring 
substances are hydrated oxides of iron and manganese. The former 
is scattered through the mass in a state of very fine division ; in 
some points, however, it is more localised, the argillaceous matter 
here appearing with a browner tinge, but these spots are noticed 
gradually to disappear in the surrounding mass. The coloration 
given by the manganese is much more distinct ; there are small 
rounded brownish spots with a diameter of less than 0*01 mm., 
which disappear under the action of hydrochloric acid with dis- 
engagement of chlorine. These small round concretions, which are 
probably a mixture of the oxides of iron and manganese, will be 
described with more detail in the “ Challenger ” Report. 
The following table shows the nomenclature we have adopted - 
f Shore formations, 
I Blue mud, 
I Green mud and sand, 
1 Found in inland 
! seas and along the 
shores of con- 
tinents. 
Terrigenous I Red mud, 
deposits. ^ , 
^ ( ;n-po I miiin 
Coral mud and sand, 
Coralline mud and sand, 
Volcanic mud and sand, 
3 Found about 
• oceanic islands and 
j along the shores of 
j continents. 
" Red clay, 
I Found in the 
Pelao-io Globigerina ooze, 
(leposHs. ^ Pteropod ooze, 
I abysmal regions 
I of the ocean 
basins. 
J 
2 L 
VOL. XII. 
