THE OLDEST AIR-BREATHERS 277 



animals, with the remains of those which had fallen into the 

 deeper pits, would be imbedded in the sediment which would 

 then fill up the holes. These seem to have been the precise 

 conditions of the bed which has afforded all these remains. 



The history of a bed containing reptiliferous erect trees 

 would thus be somewhat as follows : — 



A forest or grove of the large-ribbed trees known as Sigil- 

 larice^ was either submerged by subsidence, or, growing on low 

 ground, was invaded with the muddy waters of an inundation, 

 or successive inundations, so that the trunks were buried to 

 the depth of several feet. The projecting tops having been 

 removed by subaerial decay, the buried stumps became hollow, 

 while their hard outer bark remained intact. They thus be- 

 came hollow cylinders in a vertical position, and open at top. 

 The surface having then become dry land, covered with vegeta- 

 tion, was haunted by small quadrupeds and other land animals, 

 which from time to time fell into the open holes, in some cases 

 nine feet deep, and could not extricate themselves. On their 

 death, and the decomposition of their soft parts, their bones 

 and other hard portions remained in the bottom of the tree 

 intermixed with any vegetable debris or soil washed in by rain, 

 and which formed thin layers separating successive animal 

 deposits from each other. Finally, the area was again sub- 

 merged or overflowed by water, bearing sand and mud. The 

 hollow trees were filled to the top, and their animal contents 

 thus sealed up. At length the material filling the trees was by 

 pressure and the access of cementing matter hardened into 

 stone, not infrequently harder than that of the containing beds, 

 and the whole being tilted to an angle of 20°, and elevated into 

 land exposed to the action of the tides and waves, these singular 

 coffins present themselves as stony cylinders projecting from 

 the cliff or reef, and can be extracted and their contents 

 studied. 



The singular combination of accidents above detailed was, 



