142 WHAT MAY BE LEARNED FROM EOZOON 



In some beds of greensand every grain seems to have been 

 moulded into the interior of a microscopic shell, and has re- 

 tained its form after the frail envelope has been removed. In 

 some cases the glauconite has not only filled the chambers 

 but has penetrated the fine tubulation, and when the shell is 

 removed, either naturally or by the action of an acid, the 

 silicious fillings of the interior of the tubes project in 

 minute needles or bundles of threads of marvellous delicacy 

 from the surface of the cast. It is in the warmer seas, and 

 especially in the bed of the Egean and of the Gulf Stream, that 

 such specimens are now most usually found. 1 If we ask why 

 this mineral glauconite should be associated with foraminiferal 

 shells, the answer is that they are both products of one kind 

 of locality. The same sea bottoms in which Foraminifera 

 most abound are also those in which the chemical conditions 

 for the formation of glauconite exist. Hence, no doubt, the 

 association of this mineral with the great foraminiferal forma- 

 tion of the chalk. It is indeed by no means unlikely that the 

 selection by these creatures of the pure carbonate of lime from 

 the sea water or its minute plants, may be the means of setting 

 free the silica, iron, and potash, in a state suitable for their 

 combination. Similar silicates are found associated with 

 marine limestones, as far back as the Cambro-Silurian age; 

 and Dr. Sterry Hunt, than whom no one can be a better 

 authority on chemical geology, has argued on chemical grounds 

 that the occurrence of serpentine with the remains of Eozoon 

 is an association of the same character. 



However this may be, the infiltration of the pores of Eozoon 

 with serpentine and other silicates has evidently been one main 

 means of its preservation. When so infiltrated no meta- 

 morphism short of the complete fusion of the containing rock 



1 Beautiful specimens of Nummulites preserved in this way, from the 

 Eocene of Kumpfen in Bavaria, have been communicated to me through the 

 kindness of Dr. Otto Hahn. 



