§ 23. CLIMATE INDICATED BY FOSSIL WOOD. 697 



native of Norfolk Island, a small spot in the South Pacific, 

 about fifteen miles in circumference. This island presents 

 a scene of the most luxuriant vegetation, and abounds in this 

 particular group of pines, some of which attain a height of 

 two hundred feet, and a circumference of thirty. 



Even in the foliage of the plants of the different families, 

 there are such obvious distinctive characters, that the 

 botanist can often, from a mere fragment of a leaf, detect 

 the dicotyledonous structure in the fibrous interlacing of 

 its vessels, as in that of the oak ; and the monocotyledonous, 

 in the smooth parallel veins in that of the lily. The appli- 

 cation of these principles to the investigation of the fossil 

 remains of vegetables we may now consider. 



23. Climate and Seasons indicated by Fossil Wood. 

 — In the course of these Lectures, it has been demonstrated 

 how, by a knowledge of comparative anatomy, the form, 

 structure, and economy of beings long since obliterated 

 from the face of the earth, may with certainty be deter- 

 mined; in like manner, by the aid derived from a few 

 botanical principles, we may not only discover the form and 

 character of vegetables, of which but the faintest vestiges re- 

 main, but also point out important inferences relating to the 

 state of the earth, the nature of the climate, and even of the 

 seasons which prevailed at the periods w r hen those plants 

 flourished. Our distinguished countryman, Professor Bab- 

 bage, has admirably exemplified the inductive process by 

 which such results may be obtained : — 



" We have seen, that dicotyledonous trees increase in size by the 

 deposition of an additional layer annually between the wood and the 

 bark ; and that a transverse section of such trees presents the appear- 

 ance of a series of nearly concentric, irregular rings, the number of 

 which indicates the age of the tree. The relative thickness of these 

 annular markings depends on the more or less flourishing state of the 

 plant during the years in which they were formed. Each ring may, in 

 some trees, be observed to be subdivided into others, thus indicating 

 successive periods of the same year during which its vegetation was 

 advanced or checked. These rings are disturbed in certain parts by 



