Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/371

 CONIFERÆ IN THE SECONDARY SERIES. these modifications of the existing Family of Coniferæ date their commencement from that very ancient period, when the Carboniferous strata of the Transition formation were deposited.

Fragments of trunks of Coniferous wood, and occasionally leaves and cones occur through all stages of the Oolite formation, from the Lias to the Portland stone. On the upper surface of the Portland stone, we find the remains of an ancient forest, in which are preserved large prostrate silicified stumps of Coniferæ, having their roots still fixed in the black vegetable mould in which they grew. Fragments of coniferous wood are also frequent throughout the Wealden and Greensand formations, and occur occasionally in Chalk.

It appears that the Coniferæ are common to fossiliferous strata of all periods; they are least abundant in the Transition series, more numerous in the Secondary, and most frequent in the Tertiary series. Hence we learn that there has been no time since the commencement of terrestrial vegetation on the surface of our Globe, in which large Coniferous trees did not exist; but our present evidence is insufficient, to ascertain with accuracy the proportions they bore to the

(Pl. 56s, Fig. 6. a) the longitudinal section has the characters of Araucaria. (Pl. 56a, Fig. 3, 5.) So also those Coniferæ of the great Coal formation of Edinburgh and Newcastle, which exhibit the structure of Araucaria in their longitudinal section, have no distinct concentric layers; whilst in the fossil Coniferæ from the New Holland and Nova Scotia Coal-field, both longitudinal and transverse sections agree with those of the recent tribe of Pinus.

Mr. Witham also observes that the Coniferæ of the Coal formation, and mountain limestone group, have few and slight appearances of the concentric lines, by which the annual layers of the wood are separated, which is also frequently the case with the Trees of our present tropical regions, and from this circumstance conjectures that, at the epochs of these formations, the changes of season, as to temperature at least were not abrupt.