260 



LYELL'S ELEMENTS OF GEOLOGY. 



&ate of Deposition of the Coal Strata. 



Fig. 271. 



Inclined position of a fossil tree cutting through 

 horizontal beds of sandstone, Craigleith quarry. 

 Edinburgh. Angle of inclination from a to 

 b, 27. 



coal, forming a striking 

 contrast in colour with the 

 white quartzose sandstone 

 in which it lay. The an- 

 nexed figure represents a 

 portion of this tree, about 

 15 feet long, which I saw 

 exposed in 1830, when all 

 the strata had been re- 

 moved from one side. The 

 beds which remained were 

 so unaltered and undis- 

 turbed at the point of 



junction, as clearly to show that they had been tranquilly depo- 

 sited round the tree, and that the tree had not subsequently 

 pierced through them, while they were yet in a soft state. They 

 were composed chiefly of siliceous sandstone, for the most part 

 white ; and divided into laminae so thin, that from six to four- 

 teen of them might be reckoned in the thickness of an inch. 

 Some of these thin layers were dark, and contained coaly mat- 

 ter; but the lowest of the intersected beds were calcareous. 

 The tree could not have been hollow when imbedded, for the 

 interior still preserved the woody texture in a perfect state, the 

 petrifying matter being, for the most part, calcareous.* It is 

 also clear, that the lapidifying matter was not introduced late- 

 rally from the strata through which the fossil passes, as most of 

 these were not calcareous. It is well known that, in the Missis- 

 sippi and other great American rivers, where thousands of trees 

 float annually down the stream, some sink with their roots down- 

 wards, and become fixed in the mud. Thus placed, they have 

 been compared to a lance in rest ; and so often do they pierce 

 through the bows of vessels which run against them, that they 

 render the navigation extremely dangerous. But the vertical 

 coal-plants did not always retain their roots. Perhaps they sank 

 with their larger end downwards, because the specific gravity of 

 the wood may have been greatest near the lower end. In trees 

 of the Endogenous class, in particular, the wood of the inferior 

 and older part of the trunk is more dense than the upper and 

 younger portions ; and if the former should become water-logged 

 while the upper part of the stem still remained nearly as light 

 as water, or even lighter, not only would the whole trunk descend 

 perpendicularly, but when it reached the bottom it might stand 

 upright, provided a very slight support was afforded to its lower 



See figures of texture, Witham, Foss. Veget., pi. 3. 



