of Edinburgh, Session 1883-84. 
505 
We usually took a gramme of a mean sample of the substance for 
this purpose, using weak and cold hydrochloric acid. However, as 
the deposits often contain carbonates of magnesia and iron as well, 
the results calculated by associating the carbonic acid with the 
lime are not perfectly exact, but these carbonates of magnesia and 
iron are almost always in very small proportion, and the process is, 
M^e think, sufficiently accurate, for, owing to the sorting of the 
'elements which goes on during collection and carriage, no two 
samples from the same station give exactly the same percentage. 
The number which follows the words Carbonate of Calcium ” indi- 
cates the percentage of CaCOg ; v/e then give the general designa- 
tions of the principal calcareous organisms in the deposit. 
The part insoluble in the hydrochloric acid, after the deter- 
mination of the carbonic acid, is designated in our descriptions 
“ Residue^ The number placed after this word indicates its per- 
centage in the deposit; then follow the colour and principal 
physical properties. This residue is washed and submitted to 
decantations, which separate the several constituents according to 
their density; these form three groups — (1) Minerals, (2) Siliceous 
Organisms, (3) Fine Washings. 
1. Minercds. — The number within brackets indicates the percent- 
age of particular minerals and fragments of rocks. This number is 
the result of an approximate evaluation, of which we will give the 
basis in our report. As it is important to determine the dimensions 
of the grains of minerals which constitute the deposit, we give, 
after the contraction m. di.^ their mean diameter in millimetres. 
We give next the form of the grains, if they are rounded or angular, 
&c. ; then the enumeration of the species of minerals and rocks. 
In this enumeration we have placed the minerals in the order of 
the importance of the role which they play in the deposit. The 
specific determinations have been made with the mineralogical 
microscope in parallel or convergent polarised light. 
2. Siliceous Organisms.~Th.& number between brackets indicates 
the percentage of siliceous organic remains ; we obtain it in the 
same manner as that placed after the word Minercds, The siliceous 
organisms and their fragments are examined with the microscope 
and determined. We have also placed under this heading the 
glauconitic casts of the Foraminifera and other calcareous organisms. 
