A remarkable picture of the conditions of Palæozoic land life is presented by the occurrence of remains of reptiles, millepedes and land-snails in such erect trees as that represented in Fig. 140. In the now celebrated section of the South Joggins in Nova Scotia, trees of this kind occur at more than sixty different levels; but only in one of these have they as yet been found to be rich in animal remains. Fortunately this bed is so well exposed and so abundant in trees, that I have myself, within a few years, removed from it about twenty of them, the greater number affording remains of land animals. [Illustration: FIG. 140.—Section showing the position of an erect _Sigillaria_, containing remains of land animals. 1. Underclay, with rootlets of _Stigmaria_, resting on gray shale, with two thin coaly seams. 2. Gray sandstone, with erect trees, _Calamites_, and other stems: 9 feet. 3. Coal, with erect tree on its surface: 6 inches. 4. Underclay with _Stigmaria_ rootlets. _a_, _Calamites_. _b_, Stem of plant undetermined. _c_, _Stigmaria_ roots. _d_, Erect trunk, 9 feet high.] The history of one of these trees may be shortly stated thus. It was a _Sigillaria_, perhaps two feet in diameter, and its stem had a dense and imperishable outer bark, a soft cellular inner bark liable to rapid decay, and a slender woody axis not very durable. It grew on the surface of a swamp, now represented by a bed of coal. By inundations and by subsidence, this swamp was exposed to the invasion of muddy and sandy sediment, and this went on accumulating until the stem of the tree was buried to the height of about nine feet, before which time it was no doubt killed. After a time the top decayed and fell, leaving the buried stump imbedded in the sandy soil, which had now become dry, or nearly so. The trunk decayed, its inner bark and axis rotting away and falling in shreds into the bottom of the cylindrical hole, about nine feet deep, once occupied by the stem, and now kept open like a shaft or well by the hard resisting outer bank. The ground around this opening became clothed with ferns and reed-like _Calamites_, partly masking and concealing it. And now millepedes and land snails made the buried trunk a home, or fell into it in their wanderings; and small reptiles sporting around, in pursuit of prey, or themselves pursued, stumbled into the open pitfall, and were unable to extricate themselves, though I have found in some of the layers in these trees trails which show that these imprisoned reptiles had wearily wandered round and round, in the vain search for means of exit, till they died of exhaustion and famine. The bones of these dead reptiles, shells of land-snails and crusts of millepedes, accumulated in these natural coffins, and became mixed with vegetable debris falling into them, and with thin layers of mud washed in by the rains; and this process continued so long that a layer of six inches to