158 RELICS OF PRIMEVAL LIFE 



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

 tends into the finer tubuli of the surfaces of the 

 laminae. 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 





■^~^s§;^^Z^^ 



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



are rarely perfect or fully infiltrated. Even the 

 coarser canals are not infrequently imperfect, while 

 the laminae themselves are sometimes crumpled, 

 crushed, faulted, or penetrated with veins of chr)-- 

 sotilc or of calcite. In some instances the cal- 

 careous lamin.ne are replaced by dolomite, in which 

 case the canal-systems are always imperfect or 

 obsolete. The laminae of the test itself are also in 



