256 
PROGRESS OF MICROSCOPICAL SCIENCE. 
found Dr. Wyville Thomson thought ho could trace it to some great 
river, such as the Amazon, or to the fine deposit brought down by 
somo great river ; but he found on further research that he did not 
get it near the land, for where the water shallowed he did not get it, 
and he came to the conclusion that it could not be accounted for by 
any river action whatever. He then formed an idea that it might be 
what lie called the ash of the shells of the Foraminifcra, which was 
now believed to be diffused in enormous masses over the whole bottom 
of the deep Atlantic. There was first on the surface what Dr. 
Carpenter believes to bo living Globigcrimc ; then, below that, what 
was called ooze, in which not so much the shells as fragments of 
them wero found, and a large quantity of white impalpable matter, 
forming a very fine white mud, which was certainly the result of the 
gradual disintegration of the shells. Then at further depths below 
that, Dr. Thomson, finding this red mud, formed the hypothesis that 
at great depths there was an excess of carbonic acid, and under great 
pressures with this excess of carbonic acid the calcareous portion of 
the shell was dissolved and any mineral matter that was not calcareous 
was left behind. This mud silicate of iron and alumina was analyzed, 
as also a portion of the ooze, when it was found by Dr. Thomson that 
after removing the. calcareous portion and dissolving it by dilute acid, 
a residue of the same kind was obtained, namely, silicate of iron and 
alumina, and upon that basis he put forward the speculation that this 
red ash was simply the ash of the shells of these Globigerinae and Fora- 
minifera. It seemed to the lecturer that this was not the most likely 
explanation of it. In the first place he had no reason to believe that 
any ash at all was left behind when the pure shells were dissolved in 
dilute acid. He believed they would give as pure carbonate of lime 
mixed with animal matter as could be obtained anywhere. But then 
another source occurred to him. It was shown many years ago that 
most green sands occurring in all geological periods from the Silurian 
downwards, when examined by the microscope, were found to be 
really internal casts of Foraminifcra. In consequence of this dis- 
covery, and of the discovery by the late Professor Bailey, of New 
England, that the same thing was found in recent Foraminifera, Dr. 
Carpenter and others associated with him found exactly the same 
thing with foraminiferous forms, namely, that by dissolving away 
the shell, they could get in some instances green silicates, and in 
other instances ochry silicates, giving the form of the animal. 
Chemists all agreed that this deposit took place by a process of 
chemical substitution, although they were not all agreed as to the 
precise mode in which it occurred. They all agreed, however, that 
it was through the decomposition of the animal that the silicates were 
precipitated from sea water, and that they took the place of the 
animal substances particle by particle, filling completely the cavities 
of these minute shells with green or ochry silicates, and thus giving 
perfect models of the animal. Among Admiral Spratt’s dredgings in 
the ‘ iEgean ’ it happened that Dr. Carpenter had some internal casts 
which were a bright red, and also some which showed the transition 
from green to oclireous — a green core and a sort of ochreous eftlores- 
