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PRINCIPLES OF STRATIGRAPHY 



diameter at the base and nine feet in height. In the lower part of 

 many of these erect trees there is a deposit of eartliy matter black- 

 ened with carbon and vegetable remains and richly stored with bones 

 of small reptiles, land snails and millipedes." Dawson considers 

 that "on decay of the woody axis and inner bark they must have 

 constituted open cylindrical cavities, in wiiich small animals shel- 



FiG. 116. Buried peat bed near Marquette. Micliigan, with bog-iron stratum 

 below and sand dune above. Exposure made by easterly storm. 

 (After Davis.) a. stump of buried tree; b, sand stratum, with 

 roots and other plant remains; c. e. and g, pine needles; d, 

 sand with grass remains ; f, iron sand ; It, pure sand, cross- 

 bedded ; i, peat stratum, with standing pine stump ; k, bog iron. 

 (Height of section about 15 feet.) 



tered themselves, or into which they fell and remained imprisoned. 

 These natural traps must have remained open for some time on a 

 subaerial surface." Fifteen out of twenty-five erect trees proved 

 to have these contents, in one no less than twelve reptilian skeletons 

 occurring. In a few instances portions of the cuticle, ornamented 

 with horny scales and spines, had been preserved. In these de- 

 posits, it is evident that the trees after being buried up to a certain 

 depth rotted away on the surface or were blown down, and that 



