94 



DYNAMICAL GEOLOGY. 



carbonate) is deposited in the lower part as high as about 

 the region of the stomach, as shown in Fig. 46. When 

 the animal seems to disappear, it only withdraws the soft 

 upper parts within the stony lower part. But the stony 

 material is everywhere within the living organic matter 

 and covered. When the living organic matter is taken 



FIG. 46. Ideal section of a single living coral. The shaded portion contains 

 carbonate of lime. 



away, as in dead corals, then we have only the radiated 

 structure of the lower part in stone. This is well shown 

 in Fig. 47, a and I. The corals which form reefs, how- 

 ever, are individually extremely small. 



FIG. 47. a, stony part of a single coral ; ft, section of same, showing structure. 



Compound Coral, or Corallum. Many lower ani- 

 mals, like plants, have the power of reproducing by buds. 

 If the buds separate, they form distinct individuals ; but 



