98 



THE DAWN OP LIFE. 



It is from a sketch by Dr. Carpenter, and shows the 

 delicate canals partly filled with calcite as clear and 



fra. 23. Slice of Crystalline Lower Silurian Limestone ; showing 

 Crinoids, Bryozoa, and Corals in fragments. 



FIG. 24. Wall of Eozoon penetrated with Canals. The unshaded 

 portions filled with Calcite. (After Carpenter.) 



colourless as that of the shell itself, and distinguish- 

 able only by careful management of the light. 



In the case of recent and fossil Foraminifers, these 

 when not so little mineralized that their chambers 



