109 



markingt> of the outer wood, and even of the bark, are often found 

 impressed so distinctly on these erect sandstone casts as to afford 

 a means of discriminating the character of the plant. 



It seems therefore undeniable, that in these cases the mass of 

 sediment, amounting sometimes to twenty-five feet, was accumu- 

 lated around the standing tree in a very short time, a mere mo- 

 ment as compared with the units according to which geologists 

 are accustomed to reckon the growth of such deposits, in the usual 

 way of sedimentary accumulation. Yet a little consideration will 

 show, that facts of this kind furnish no support to the opinion of 

 those whose imperfect acquaintance with geological data have led 

 them to deny the necessity of prolonged cycles of formative action 

 in the production of the great systems of sedimentary strata. 



In explaining the rapid entombment of the trees in their verti- 

 cal position, it should be borne in mind that there are two pro- 

 cesses very distinct from each other by which sediment may be 

 accumulated over a given area. One of these is the series of 

 actions by which the materials of preexisting rocks, worn down, 

 and diffused by tides and currents, are deposited more or less 

 equally over wide regions, so as to build up step by step a newer 

 system of formations. The other consists in the transfer of sedi- 

 ment already accumulated, from one part of the bed of the sea or 

 estuary to a neighboring one. In the former process it would 

 seem clear, from all the geological data, that vast periods of time 

 must have been consumed. The latter beino; nothins; more than 

 the sweeping of soft sand and mud from one submerged area to 

 another in its vicinity, would require no other agency than some 

 unusual local disturbance of the waters, such as might result from 

 earthquakes or great inundations, and would demand but a short 

 time for its completion. In this view, the thick mass of sand- 

 stone and shale inclosing the erect trunk of the fossil tree, al- 

 though accumulated at this particular part of the carboniferous 

 area in a very short time, is not to be regarded as simply the pro- 

 duct and measure of this brief geological moment. Considered in 

 relation to its previous history in the carboniferous period, it 

 rather represents the comparatively long series of combined 

 actions which brought its materials into suspension in the waters, 

 and gradually deposited them over the area, from which they 

 were afterward so rapidly removed. 



