266 THE POPULAR SCIENCE MONTHLY. 



Hydrous silicates act as mineralizers elsewhere than in the green- 

 sand. Crinoidal joints from the Silurian limestones of New Brunswick 

 have been saturated by it, filling all the interstices, and smell mollusks 

 from Wales have had their interior permeated by it. There is much 

 variation in the composition of these infiltrating silicates. Some from 

 the calcaire grassier, near Paris, approach serpentine. Others carry 

 magnesia. Those from the Lower Silurian of the Upper Mississippi 

 Valley are like glauconite. In the Eozoon, as described above, ser- 

 pentine, which is a hydrous silicate of magnesia, replaces the supposed 

 sarcodous or animal part of the structure. It has thus (jorresponded 

 to the glauconite of the present day filling the canals of the supple- 

 mentary skeleton, the tubuli of the shell, and replacing the softer ani- 

 mal portions. Pyroxene and Loganite also replace the animal matter 

 in the Canadian Laurentian fossils, and in the Eozoon discovered in 

 the supposed Montalban series of Ontario carbonate of lime is the min- 

 eralizer. These last-named specimens were not described till 1867; 

 and, as they exhibit the foraminiferal structure without the presence 

 of any form of silicate, they completely establish the genuineness of 

 the fossil. In Bavaria Giimbel states that chondrodite, hornblende, 

 and scapolite, and perhaps other minerals, should be added to the list 

 of silicates petrifying the Eozoon. 



The objections that have been made to the organic character of 

 Eozoon relate chiefly to the close resemblances between mineral and 

 organic replacement, or between pseudomorphs and petrifactions. 

 Other resemblances are to dendritic and concretionary structures. In- 

 asmuch as these structures represent the higher efforts of the mineral 

 kingdom in crystallization and the nearest approach to the inorganic 

 world allowed by animal forms, it is not strange that the two extremes 

 should resemble each other sufficiently to deceive practical observers. 

 The canal system maybe almost the very picture of certain dendrites. 

 The latter, however, usually occupy a flat surface like moss-agates ; 

 whereas the former branch out in every direction, as appears in Fig. 

 5, projecting upward and downward, as well as sideways. 



Organisms are preserved because of the more or less complete sub- 

 stitution of mineral for animal matter. Pieces of coal or wood that 

 have been deposited in clay may be washed out, but the small pores 

 and interstices will be seen to be filled with the matrix. When the 

 burial has been in a solution capable of precipitating solid matter, the 

 wood will be found more or less changed according to the nature of 

 the solution and its capacity for alteration. Some specimens become 

 nearly pure agate in consequence of the gradual substitution, particle 

 by particle, of the organic matter by silica. Fig. 6 shows different 

 stages of petrifaction in coniferous wood: a is a small fragment where 

 the pores have been filled with silica, assuming a somewhat rhomboidal 

 appearance, and the black parts represent the woody substance, still 

 intact ; in b the vegetable matter is wanting, having rotted away, 



