It is now many years since the operations of the quarryman in the carboniferous sandstones of Edinburgh and Newcastle disclosed the remains of huge gnarled trunks deeply imbedded in the rock. The neighbourhood of the latter town yielded, in 1829,[24] the stem of a tree seventy-two feet long, without branches, but roughened with numerous knobs, indicative of the places whence branches had sprung. At Craigleith, near Edinburgh, a trunk thirty-six feet long, and three feet in diameter at the base, was disinterred in the year 1826. Since then, several others have been found in the same neighbourhood; some of them sixty and even seventy feet in length, and from two to six in breadth. They were, for the most part, stripped of roots and branches, and lay at a greater or less angle among the white sandstone beds, which they cut across obliquely. It was unknown for some time to what division of the vegetable kingdom these trunks should be referred. Their irregular branched surface and undoubted bark indicated a higher kind of structure than that possessed by any of the other carboniferous plants; but the conjecture remained unverified until an ingenious and beautiful method was discovered of investigating their internal organization. Two Edinburgh geologists, Mr. Nichol and Mr. Witham, succeeded in obtaining slices of the plants sufficiently transparent to be viewed under the microscope by transmitted light, and in this way their true structure was readily perceived. The method of preparing these objects was simply as follows:--A thin slice of the plant to be studied was cut by the lapidary, or detached by the hammer. One side having been ground down smooth, and polished, was cemented by Canada balsam to a piece of plate-glass, and the upper surface was then ground down and polished in like manner, so as to leave the slice no thicker than cartridge-paper.[25] When the preparation was then placed under a magnifying power, the minute cells and woody fibre of the plant could be detected as clearly as those of a recent tree. The Craigleith fossils were in this way recognised as belonging to the great coniferous family, and to that ancient[26] division of it which is, at the present day, represented by the pine of Norfolk Island--"a noble araucarian, which rears its proud head from 160 to 200 feet over the soil, and exhibits a green and luxuriant breadth of foliage rare among the coniferæ."[27] Some of these plants have yielded faint traces of the annual rings shown so markedly in the cross section of our common forest-trees; whence it would appear, that even as far back as the times of the coal-measures, there were seasons of alternate heat and cold, though probably less defined than now. [Footnote 24: Witham's _Foss. Veget._ p. 31.] [Footnote 25: For a more detailed description of the process, see Witham's _Foss. Veget._ p. 45.]