SECT. ii. FOSSIL EOZOON. 55 



The fossil Eozoon consists of a succession of parallel 

 rows or tiers of chambers, in which the sarcode of the 

 living animal had been replaced by a siliceous infiltra- 

 tion, so that when the calcareous shell was destroyed 

 by dilute acid, the cast was found to be precisely like 

 that of a JSummulite ; thin slices of it taken in dif- 

 ferent directions being examined with a microscope, it 

 was found that the siliceous matter had not only filled 

 that portion of the chambers which had been occupied by 

 the sarcode-body of the animal and the canal-system, but 

 had actually taken the place of the pseudopodial threads, 

 the softest and most transitory of living substances, 

 which were put forth through tubuli in the shell- walls 

 of less than the T^Q-Q-Q P ar ^ of an inch in diameter. 

 6 These are the very threads themselves turned into 

 stone by the substitution which took place, particle by 

 particle, between the sarcode body of the animal and 

 certain constituents of the water of the ocean, before 

 the destruction of the sarcode by ordinary decompo- 

 sition.' 9 The shell had an intermediate skeleton, but 

 the minute tubes in the walls of the chambers are 

 so characteristic of the Nummulites, that they were 

 sufficient alone to determine the relationship of the 

 Eozoon to its modern representative. 



The external shape and limits to the size of the 

 individual Eozoon have not been determined with 

 certainty, on account of its indefinite mode of growth, 

 and the manner in which the fossilized masses are 

 connected with the highly crystalline matrix in which 

 they are imbedded ; there is no doubt, however, that they 

 spread over an area of a foot or even more, and attained 

 a thickness of several inches. As they seem to have f 

 increased laterally by buds which never fell off, they ( 

 formed extensive reefs ; at the same time they had a / V 

 vertical growth, for in some of the reefs the older / 



8 Dr. Carpenter. 



