§ 45. CONCLUDING REMARKS. 



657 



forms in which the Crinoidea appear in the natural records 

 of our planet. 



And here I must conclude this very general notice of 

 this interesting family of Crinoideans, which is of exces- 

 sive rarity in the present seas, but swarmed in the ocean of 

 the Silurian epoch, in various modifications of form and 

 structure, all of which are now extinct. 



45. Concluding remarks. — From this review of the 

 Polyparia and Crinoidea, we learn that an atom of living 

 jelly floating in the ocean, and at length becoming affixed 

 to a rock, may be the first link in a chain of events, which, 

 after the lapse of ages, may produce important modifications 

 in the physical geography of our globe. We have seen 

 that the living polypes in their rocky habitations enjoy all 

 the blessings of existence, and at the same time are the 

 unconscious instruments of stupendous operations, which in 

 after ages may affect the destinies of mighty nations ; and 

 that the materials elaborated by their agency, and subse- 

 quently consolidated by chemical changes, may become the 

 foundations of Islands and Continents, and constitute new 

 and favourable sites for the abode of future generations of 

 the human race. 



And when we bring the knowledge thus acquired to bear 

 on the natural records of our planet, and examine the rocks 

 and mountains around us, w r e find that in periods so remote 

 as to exceed our powers of calculation, similar effects were 

 produced by beings of the same type of organization as 

 those whose labours have been the subject of our contem- 

 plation. We are thus enabled to read the history of the 

 past, and to trace the succession of events, each of such 

 duration as to defy all attempts to determine with any 

 approach to probability the period required for its develop- 

 ment. 



In fine, these investigations have shown us the marvel- 

 lous structure of creatures invisible to the naked eye, their 



