142 THE STORY OP THE EARTH AND MAN. 



Sigillarias growing on a low flat. This becomes 

 submerged by subsidence or inundation, the soil is 

 buried under several feet of sand or mud, and the 

 trees killed by this agency stand up as bare and 

 lifeless trunks. The waters subside, and the trees 

 rapidly decay, the larvae of wood-boring insects per- 

 haps aiding in the process, as they now do in the 

 American woods. The dense coaly outer bark alone 

 resists decomposition, and stands as a hollow cylinder 

 until prostrated by the wind or by the waters of 

 another inundation, while perhaps a second forest or 

 jungle has sprung up on the new surface. When it 

 falls, the part buried in the soil becomes an open hole, 

 with a heap of shreds of wood and bark in the bottom. 

 Such a place becomes a fit retreat for gally-worms 

 and l^nd- snails; and reptiles pursuing such animals, 

 or pursued by their own enemies, or heedlessly 

 scrambling among the fallen trunks, may easily fall 

 into such holes and remain as prisoners. I remember 

 to have observed, when a boy, a row of post-holes 

 dug across a pasture-field and left open for a few days, 

 and that in almost every hole one or two toads were 

 prisoners. This was the fate which must have often 

 befallen the smaller reptiles of the coal forests in the 

 natural post-holes left by the decay of the Sigillarias. 

 Yet it may be readily understood that the combination 

 of circumstances which would efi'ect this result must 

 have been rare, and consequently this curious fact has 

 been as yet observed only in the coal formation of 

 Nova Scotia; and in it only in one locality, and in 



