1914-15.] Fossil Micro-organisms. ’ 131 
rock. The membranes of this organism were plentifully coated with ferric 
hydroxide, and it was evident that in all 4 slides the organism was the 
same, viz. the one to which the name Phycomycites Frodinghamii has been 
given. It was further obvious that, in the case of the rocks in which the 
organism was found, the formation of the rock was quite independent 
of the presence of this organism. It simply meant that a number of the 
organic particles which had been cemented together were composed of 
bodies in a state of putrefaction instead of having been free from putre- 
factive organisms. The only difference that the presence of the putrefactive 
organisms effected was, that by their presence the stone had become slightly 
richer in iron. As rock-builders they must be barred out altogether. So 
far as my observations on the ironstones of Great Britain go, the iron- 
organism has simply affected the material of which the rock is made, just 
as dry-rot might affect the wood which is to be used for constructive pur- 
poses. The construction does not depend for its existence on the dry-rot, 
and neither does the rock depend for its formation on the presence of the 
iron-organism ; though both are affected, the one by the presence of the 
dry-rot and the other by the presence of the iron-organism. We may 
therefore sum up the whole situation by stating that, with the exception 
of the four samples cited by Molisch, there is no known instance of a 
ferruginous rock which owes its existence primarily to the presence of 
iron-organisms ; and with regard to the rocks in which iron-organisms 
were found by Molisch, the evidence is too scanty at present to permit of 
definite conclusions on the matter. 
Summary. 
The work embraces the results of the systematic examination, for fossil 
micro-organisms, of slides prepared from ironstones and ferruginous lime- 
stones from various districts of Great Britain. 
Abundant traces were found in the Frodingham Ironstone of a fossil 
fungus allied to the modern Phycomycetes. This is named Phycomycites 
Frodinghamii. The traces include hyphse, sporangia, and spores. These 
are described, measured, and photographed, and details of the life-history, 
so far as ascertainable, are given. 
In the Secondary rocks of the island of Raasay (N.W. Scotland) a 
fungus, provisionally called Palceomyces a, was found and is described. 
In the Dunliath Ferruginous Limestone a fossil Actinornycete, provision- 
ally called Actinomy cites a, was found and is described. 
From the Cretaceous rocks the remains of fossil bacteria were obtained. 
