698 



THE WONDERS OF GEOLOGY. Lect. VII. 



irregularities resulting from branches ; and the year in which each 

 branch first sprang from the parent stock, may therefore be ascertained 

 by proper sections. These prominent effects are obvious to our senses ; 

 but every shower that falls, every change of temperature that occurs, 

 and every wind that blows, leaves on the vegetable world the traces of 

 its passage ; slight, indeed, and imperceptible perhaps to us, but not 

 the less permanently recorded in the depths of those woody fabrics. 



" All these indications of the growth of the living tree are preserved 

 in the fossil trunk, and with them also frequently the history of its 

 partial decay. Let us now examine the use we can make of these 

 details relative to individual trees, when considering forests submerged 

 by seas, imbedded in peat mosses, or transformed, as in some of the 

 harder strata, into stone. Let us imagine that we possessed sections 

 of the trunks of a considerable number of trees, such as those occurring 

 in the stratum called the Dirt-bed in the Island of Portland (ante, 

 p. 386). If we were to select a number of trees of about the same size, 

 we should possibly find many of them to have been contemporaries. 

 This fact would be rendered probable if we observed, as we doubtless 

 should do, on examining the annual rings, that some of them, con- 

 spicuous for their size, occurred at the same distances of years in several 

 trees. If, for example, we found on several trees a remarkably large 

 annual ring, followed at the distance of seven years by a remarkably 

 thin ring, and this again, after two years, succeeded by another large 

 ring, we should reasonably infer from these trees, that seven years after 

 a season highly favourable to their growth, there had occurred a season 

 unfavourable to them : and that after two 'more years, another very 

 favourable season had happened, and that all the trees so observed had 

 existed at the same period of time. The nature of the season, whether 

 hot or cold, wet or dry, would be known with some degree of probabi- 

 lity, from the class of tree under examination. This kind of evidence, 

 though slight at first, receives additional and great confirmation by 

 the discovery of every new ring which supports it ; and, by a con- 

 siderable concurrence of such observations, the succession of seasons 

 might be ascertained in geological periods, however minute." 



24. Microscopic examination of fossil trees.* — 

 The discovery of a process by which the structure of fossil 

 vegetables can be examined with as much facility as that 

 of recent plants, has shed an unexpected light on the an- 

 cient botany of our planet. On this plate of glass you 

 perceive a thin film of a dark substance, apparently of 

 varnish. It is a slice of the blackest jet, and if held 

 * Medals of Creation, vol. i. p. 76. 



