solvent action would have destroyed the structure of these 
delicate organisms. From other internal evidence, such as 
little shells and diatomaceae, it is clear that the calcareous 
portion of this limestone has not been at any time dissolved 
to any extent, and yet such an obdurate substance as silica 
has been completely removed. Then as to the cause of its 
removal. The solution was no doubt highly calcareous, but 
we know that highly calcareous water may run over quartz 
crystals for a very long period without having the slightest 
effect upon the faces. I think that Fig. 3 will explain 
how the rods came to be so easily dissolved. This is a 
photograph of a hollow where a rod has lain which still 
contains some rounded nodules of silica. It will be seen 
from my former paper that these nodules are anhydrous 
inorganic silica, crystallizing out of the hydrated silica after 
the rod has undergone a little dehydration since it was 
alive. Now here we see the whole rod dissolved except 
such portions as were entirely mineralised, if I may use 
such a term, so that we see that the reason these silica rods 
were so easily dissolved by the calcareous solution was 
because the silica of which they were composed was in a 
hydrated easily soluble form. Thus the existence of those 
nodules which had before puzzled naturalists now gives us 
the clue to the state of the rods at the time of solution. 
Fig. 4 will still further elucidate this subject. Here it 
will be seen we have a large number of rods partially dis- 
solved. I have examined by the means given in my former 
paper above twenty samples of these partially dissolved 
rods, and I have not found one sample containing water, so 
that again we see the whole of the thoroughly mineralised 
silica is left behind, and those portions which were very 
probably hydrated dissolved. I say very probably, for we 
see that the solvent action has gone on in a very irregular 
manner and in a manner which could not be accounted for 
on any circulation hypothesis, but just in such a manner as 
