NOTES AND MEMORANDA. 
257 
cence on the surface. On another of Admiral Spratt's specimens 
there was a transition from green to red — that is, in the very same cast 
he found red in one place and green in another. It occurred to him 
that it was not improbable that this was the real origin of the red 
clay. He thought he might say it pretty certainly — and he said it on 
the authority of Professor Hofmann, who had gone carefully through 
his series — that these three colours, the green, the ochreous, and the 
red, were simply dependent on the stages of the oxidation of the iron. 
They could not be analyzed, because they were so excessively minute. 
He might mention that the ' Challenger,' near the Cape of Good Hope, 
came upon a bed of green clay, which was found to be entirely com- 
posed of these internal casts, and when that came home materials 
might be expected for a very thorough chemical analysis of these very 
curious formations. His own suggestion was that this red clay was 
not the ash of the shell, but the result of the disintegration of internal 
casts. He thought it not at all improbable that what was originally 
green or ochreous was acted upon by carbonic acid, just in the same 
manner as every chemist knows that felspar was decomposed by 
carbonic acid ; so that in the carbonic acid of the deep strata of the 
ocean, under the influence of pressure especially, there would be a 
decomposition or disintegration of these internal casts, and a higher 
oxidation of the iron giving it the red colour. It appeared to him 
that that was far more likely to be the origin of this red clay than 
its being left as an ash from the foraminiferous shells, which, as far 
as he had examined them, did not leave any ash at all. That Dr. 
Thomson should find a residue in the ooze was likely enough, because 
if some of these internal casts were formed in the Foraminifera layer, 
when all the decomposed shells were dissolved there would of course 
be the residue of these casts. It would be curious if it was referable 
to the Foraminifera at all. It was referable rather to the process by 
which the internal casts were formed, and the higher oxidation of the 
iron of them, and the disintegration formed by the action of the 
carbonic acid so as to form this deposit of red clay at the bottom. 
This seemed to him more likely than that it was formed by the 
solution of the foraminiferous shells themselves. 
NOTES AND MEMOEANDA. 
Use of the Microscope in Mineralogy. — A paper on this subject 
was read before the San Francisco Microscopical Society, and it 
appears reported in full in the ' Cincinnati Medical News' (September). 
He uses the binocular instrument and a 7|-inch objective, and he 
makes the following remarks on the subject of preparing and ex- 
amining specimens : — My method of preparing them is as follows : 
The slide is placed on a card of the same size, upon which a dot of 
ink has been made to indicate the centre. A scale of shellac is held 
T 2 
