114 Proceedings of the Koyal Society of Edinburgh. [Sess. 
all four the oolitic structure prevailed. When such a slide was closely 
examined under the microscope it was found that, while most of the frag- 
ments embedded in the calcite matrix were oolitic, a certain percentage of 
them were highly irregular in shape. Both kinds were embedded in a 
calcite matrix. The greater number of the oolitic and non-oolitic fragments 
were very small — 0’2-5’0 mm., though many were somewhat larger. 
Whilst the oolites were invariably surrounded and delimited by ferric 
hydroxide, the irregular fragments were either only partially surrounded 
by this substance, or, as in a large number of cases, were entirely free from 
it. The minute irregular fragments were of an animal nature, and repre- 
sented the last stage in the decomposition of a comparatively large animal. 
In the process the animal remains had apparently been disintegrated and 
complete severance of the fragments had evidently taken place. It was 
in the inside of these minute animal fragments that the micro-organism 
was found. In a slide in which it occurred every fragment of this kind 
was found to be packed with the hyphse of this fungus, and, from the 
completeness with which the hyphse had penetrated the tissues, it seems 
to suggest that the fungus was saprophytic on its host when the remains 
were engulfed and the fungus put out of action. The membranes of the 
hyphse were in all cases covered and impregnated with ferric hydroxide, 
and this was the case even when the edges of the animal fragments inside 
which the fungus was growing were completely devoid of the iron com- 
pound. This evidently suggests a selective absorption of iron on the part 
of the fungus, and not a mere mechanical deposition of the precipitated 
iron compound. I propose dealing further on with the claims which this 
organism possesses to be ranked among the iron-organisms. 
(c) Detailed Description of the Iron-mould. 
I. Hyphce . — In all the places where this organism was found, the hyphse 
saprophytic upon the organic fragments of the ore were of two dimensions, 
a larger measuring roughly about /x, and a smaller measuring about 2 a. 
There were variations from these dimensions caused by variation in the 
amount of deposited ferric hydroxide. These figures represent the average 
dimensions of the hyphse together with the iron deposited on their surface. 
To obtain an approximation to the dimensions of the original hyphse about 
*25 jut. would have to be subtracted from these dimensions. Evidence is 
given below to show that, as in similar modern organisms, their membranes^ 
were, shortly after death, not only covered with ferric hydroxide, but 
practically entirely replaced by this substance, so that what has been 
preserved are hollow tubes composed of ferric hydroxide. This must of 
