nt 



of 

 :h 

 r, 



■■%■ 



LAURENTIAN LIFE 



H3 



derived from the decay of their own organic 

 substance. The crystalline Trenton limestone of 

 Montreal, used there as a building stone, is an excel- 

 lent example (Fig. 22). 



It is otherwise, however, when the calcareous fossils 

 have been filled or injected with some mineral 

 matter different from the matrix, as, for example, 

 silica or some silicate, oxide or sulphide of iron. 



i%T!Tt » 



6 



« < n > I 



iiriiJ 



•♦Ml 

 If •» I 

 ••••I 



t < 1 1 » • 



ii»«f»i; 



•»<«« 





Fig. 23.~£>ta^am of different States of Fossilizalion of the Cell of a 



Tubulate Coral. 



^"^ S'"^ii^°:S"ii..S "^^'i^^^ ^'-^T^Y ^^T' «"•"- ^='-- 



conditions are found in the fosJil coLhnf,hf^ ''"r'^ ''^'",'? '"''*=^- A" '^ese 

 -Middle Permian. °^ '^^ corniferous Limestone of Canada 



In this case the texture, colour, or hardness of the 

 filling appear different from those of the limestone, 

 and may be seen in a fresh fracture or polished 

 slice ; or when the rock is weathered, the hard mine- 

 ralizing substance may project from the surface of 

 the specimens, or may be disclosed by treating the 

 surface with a weak acid. The figures here given 

 may suffice to show some of these conditions of 



8 



