OCR Text |
Show 102 FOSSlL COAL PLANTS. In vain should we attempt to explain away the phenomena of the carboniferous and other secondary formations, by supposing that the plants were drifted from equatorial seas. During the accumulation, and consolidation of so many sedimentary deposits, and the various movements and dislocations to which they were subjected at different periods, rivers and currents must often have changed their direction, and wood might as often be floated from the arctic towards tropical seas, as in an opposite direction. It is undeniable, that the materials for future beds of lignite and coal are now amassed in high latitude.s far from the districts where the forests grew, and on shores where scarcely a stunted shrub can now exist. ~he M~ckenzie~ and ~ther rivers of North America, cal'l'y pmes with their roots attached for many hundred miles towards the north, into the arctic sea, where they are imbedded in ~cltas, and some of them drifted still farther, by currents towards the pole. llut such agency, although it might account for some partial anomalies in the admixture of vegetable remains of different climes, can by no means weaken the arguments deduced from the general character of fossil vegetable remains. W c cannot suppose the leaves of tree ferns to be transported by water for thousands of miles, without being injured; nor, if this we:e. possible, would the same hypothesis explain the presence of ~nm.1ured corals and multilocular shells of contemporary origin, for t!1ese mu~t have lived in the same latitud.es where they are now mclosed m rocks. 'l"'he plants, moreover, whose remains have given rise to the coal beds, must be supposed to have grow~ upon the same land, the destruction of which provided matenals for the sandstones and con()'lomerates of that ()'roup b 0 of strata. The coarseness of the particles of many of the5c 1:o~ks attests that they were not borne from very remote locahties, but were most probably derived from islands in a vast sea, which was continuous, at that time, over a great part of the northern hemisphere, as is demonstrated by the great extent of the mountain and transition limestone formations. The same observation is applicable to many secondary strata of. a later epoch.. There must have been dry land in these latitudes, to provide materials by its disintegration for sand· s~ones,-:to afford a beach whereon the oviparous reptiles depoSlted the1r eggs,-to furnish an habitation -for the opossum of CHANGE OF CLIMATE. 103 Stonesfield, and the insects of Solenhofen. The vegetation of the same lands, therefore, must in general have imparted to fossil floras their prevailing character. From the considerations above enumerated, we must infer, that the remains both of the animal and vegetable kingdom preserved i~ strata of different ages, indicate that there has been a great diminution of temperature throughout the northern hemisphere, in the latitudes now occupied by Europe, Asia, and America. The change has extended to the arctic circle, as well as to the temperate zone. 'I.,he heat and humidity of the air, and the uniformity of climate, appear to have been most remarkable when the oldest strata hitherto discovered were formed. The approximation to a climate similar to that now enjoyed in these latitudes, does not commence till the era of the formations termed tertiary, and while the different tertiary rocks were deposited in succession, the temperature seems to have been still farther lowered, and to have continued to diminish gradually, even after the appearance of a great portion of existing species upon the earth. |