THE PALMS OF THE ANCIENT WORLD. 175 



a considerable length of time, and on the death 

 of the animals, and the decomposition of their 

 softer parts, would most likely sink to the 

 bottom, and be there interred as the sediment 

 accumulated ; as also would the shells after the 

 death of their inhabitants. It will also be 

 readily perceived that land plants, or at least 

 portions of them, especially wood, might fre- 

 quently become similarly entombed in the shal- 

 lower portions at no great distance from the 

 shore. 



Processes such as these now sketched have 

 been perpetually going on ever since this earth 

 was habitable, either for the animal or vegetable 

 creation. Guided by the relative position of 

 the strata, the lowermost being of course oldest 

 and first-formed, and also by the animal and 

 vegetable remains which they inclose, the 

 geologist has already been able to trace the 

 general outlines of a physical history of our 

 globe, and to record many of the changes which 

 have taken place upon it. 



The various eras or periods of organic life 

 upon the earth, as indicated by the strata and 

 their remains, may be stated at nine. These 

 are, — beginning with the most ancient, — 



1. The Silurian. 



2. The Devonian, (or old red sandstone.) 



