86 ' SCIENCE IN SHORT CHAPTERS. 



and only the end above ground in the water. My object 

 was to examine the condition of the buried and immersed 

 wood, and I selected this as the oldest piece I could reach. 



I found the wood very dark, the bark entirely gone, and 

 the annual layers curiously loosened and separable from 

 each other, like successive rings of bark. This continued 

 till I had stripped the stick to about half of its original 

 thickness, when it became too compact to yield to further 

 stripping. 



This structure apparently results from the easy decom- 

 position of the remains of the original cambium of each 

 year, and may explain the curious fact that so many speci- 

 mens of fossilized wood exhibit the original structure of 

 the stem, although all the vegetable matter has been dis- 

 placed by mineral substances. If this stem had been im- 

 mersed in water capable of precipitating or depositing min- 

 eral matter in very small interstices, the deposit would have 

 filled up the vacant spaces between these rings of wood as 

 the slow decomposition of the vegetable matter proceeded. 

 At a later period, as the more compact wood became de- 

 composed, it would be substituted by a further deposit, and 

 thus concentric strata would be formed, presenting a mimic 

 counterpart of the vegetable structure. 



The stick examined appeared to be a branch of oak, and 

 was so fully saturated with water that it sank rapidly upon 

 being released. 



On looking around the origin of this sub-aqueous forest 

 was obvious enough. Here and there the steep wooded 

 slopes above the lake were broken by long alleys or down- 

 ward strips of denuded ground, where storm torrents, or 

 some such agency, had cleared away the trees and swept 

 most of them into the lake. A few uprooted trees lying 

 at the sides of these bare alleys told the story plainly enough. 

 Most of these had a considerable quantity of earth and 

 stones adhering to their roots : this explains the upright 

 position of the trees in the lake. 



Such trees falling into water of sufficient depth to enable 

 them to turn over must sink root downwards, or float in an 

 upright position, according to the quantity of adhering soil. 

 The difference of depth would tend to a more rapid pene- 



