GEOLOGY. 303 



shale, an inquiry of much interest is suggested as to the rate of accumula- 

 tion of the deposit in which they are buried. Many of these erect trunks 

 are of very considerable height, and one is mentioned by Sir Charles Lyell as 

 traceable vertically across the strata for a distance of twenty-five feet. In 

 all such cases the decay of the tree could have made no great progress before 

 the trunk became buried to the whole observed depth, otherwise it would 

 have become too weak to maintain an erect position, and must have fallen 

 over. We infer, therefore, that the mass of sediment, even to the height of 

 twenty-five feet, in the case above cited, must have been accumulated around 

 the stem in a period extending at farthest only to the earlier stages of 

 change in the organic structure. Moreover, this conclusion is strongly con- 

 firmed by the fact that the peculiar markings 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 accumulated around the stand- 

 ing tree in a very short time, a mere moment 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 con- 

 sideration will show that facts of tl$s kind furnish no support to the opinion 

 of those whose imperfect acquaintance with geological data has 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 vertical position, 

 it should be borne in mind that there are two processes 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 sediment already accu- 

 mulated 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, being nothing 

 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 sandstone and shale enclosing the erect trunk 

 of the fossil tree, although accumulated at this particular part of the carbon- 

 iferous area in a very short time, is not to be regarded as simply the product 

 and measure of this brief geological moment. Considered in relation to its 

 previous history in the carboniferous period, it rather represents the com- 

 paratively 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. 



In framing any conjecture as to the length of time corresponding to the 

 formation of a group of strata at any particular locality, as the Joggins, we 

 would, of course, ascribe but a small value in years to such masses of deposit 

 as thus prove themselves to have been hastily accumulated at the spot where 

 they are found. But, on the other hand, we should be careful not to apply 

 the same measure of rapid accretion to those associated beds of shale, lime- 

 stone, coal, and even sandstone, which give intrinsic evidence of having been 



