' 



M 



158 



kELICS OF PRIMEVAL LIFE 



with a core or axis of dolomite, which also ex- 

 tends into the finer tubuli ot the surfaces of the 

 lamincTE. This, on the theory of animal origin, is 

 the most perfect state of preservation, and it equals 

 anything I have seen in calcareous organisms of 

 later periods. This state of perfection is, however, 

 naturally of infrequent occurrence. The finer tubuli 



:|! n 





■'I '^^'i 



Fig. 37. — Finest Tubuli filled with Dolomite {magnified). 



ii 1; 



:ifil ll 



are rarely perfect or fully infiltrated. Even the / 

 coarser canals are not infrequently imperfect, while 

 the lamina? themselves are sometimes crumpled, 

 crushed, faulted, or penetrated with veins of chry- 

 sotile or of calcite. In some instances the cal- 

 careous lamince are replaced by dolomite, in which 

 case the canal-systems are always imperfect or 

 obsolete. The laminae of the test itself are also in 



