the Bolton Hailway^ at Dixon Fold, near Manchester. 159 



tlirown upon shale or sandstone. The subsidence theory, on 

 the contrary, corresponds with observed facts. If the coal- 

 seams were once a mass of decayed vegetable matter, this 

 rich compost would afford the most likely soil for the growth 

 of trees, as now in tropical forests. The standing out of the 

 roots above the top of the coal seems to favour this view, 

 since the vegetable matter, as it underwent conversion under 

 pressure, would shrink from around them and leave them ex- 

 * posed ; just as in some bogs in Ireland, Mr Murchison informs 

 us (Silur. Syst., p. 559), the bases of the trunks of ancient 

 forest trees may be seen still standing in their natural posi- 

 tion, " as if on high stilts," with their roots exposed, owing 

 to the shrinking of the surrounding peat. 



Having shewn the great probability that these trees still 

 occupy their original sites, I have now to prove, 



3i/, That they became hollow from the decay of their wood, 

 and have been subsequently filled up with sedimentary de- 

 posit after immersion. 



Mr Hawkshaw, to whom we are indebted for the preserva- 

 tion of these fossils, says, in a paper read before the Geological 

 Society of London, that in the virgin forests of the torrid zone, 

 the solid wood of fallen timber trees rapidly decays, while the 

 bark retains its texture and original appearance, and that 

 in six, nine, or twelve months the wood not only decayed, but 

 altogether disappeared, so that the bark became a hollow 

 cylinder, and if struck or trodden on, readily collapsed. M. 

 Schomburgk informed me, that he repeatedly observed this 

 fact during four years travels of Surinam, especially in the 

 low and hot districts. And my friend Gardner in a letter to 

 me, dated Rio Janiero, 6th December 1840, says, " Nothing 

 is more common than to meet with the trunks of large trees 

 lying on the ground, not only in low swampy forests, but also 

 in the .dense virgin forests of mountain- tracts, covered with, 

 mosses, ferns, &;c., which to the eye appear quite sound, but 

 which in reality consist of little more than a thick bark, which 

 gives way immediately to the weight of the traveller, should 

 he incautiously step upon it." The concurring testimony of 

 these scientific naturalists, added to the many evidences we 

 possess of the high temperature of the coal era, can there- 



