Some Salient Points in the Science of the Earth

by Sir John William Dawson

A reptiliferous Tree in situ, South Joggins, N. Scotia.

This is a sketch of a tree which afforded remains of Dendrerpeton, Pupæ, etc.

The history of a bed containing reptiliferous erect trees would thus be somewhat as follows:—

A forest or grove of the large-ribbed trees known as Sigillariæ, was either submerged by subsidence, or, growing on low ground, was invaded with the muddy waters of an inundation, or successive inundations, so that the trunks were buried to the depth of several feet. The projecting tops having been removed by subaërial decay, the buried stumps became hollow, while their hard outer bark remained intact. They thus became hollow cylinders in a vertical position, and open at top. The surface having then become dry land, covered with vegetation, was haunted by small quadrupeds and other land animals, which from time to time fell into the open holes, in some cases nine feet deep, and could not extricate themselves. On their death, and the decomposition of their soft parts, their bones and other hard portions remained in the bottom of the tree intermixed with any vegetable débris or soil washed in by rain, and which formed thin layers separating successive animal deposits from each other. Finally, the area was again submerged or overflowed by water, bearing sand and mud. The hollow trees were filled to the top, and their animal contents thus sealed up. At length the material filling the trees was by pressure and the access of cementing matter hardened into stone, not infrequently harder than that of the containing beds, and the whole being tilted to an angle of 20°, and elevated into land exposed to the action of the tides and waves, these singular coffins present themselves as stony cylinders projecting from the cliff or reef, and can be extracted and their contents studied.

The singular combination of accidents above detailed was, of course, of very rare occurrence, and in point of fact we know only one set of beds at the South Joggins in which such remains so preserved occur; nor is there, so far as I am aware, any other known instance elsewhere. Even in the beds in question only a portion of the trees, about fifteen in thirty, have afforded animal remains. We have, however, thus been enabled to obtain specimens of a number of species which would probably otherwise have been unknown, being less likely than others to be preserved in properly aqueous deposits. Such discoveries, on the one hand impress us with the imperfection of the geological record; on the other, they show us the singular provisions which have been made in the course of geological time for preserving the relics of the ancient world, and which await the industry and skill of collectors to disclose their hidden treasures.

I may add that I believe all the trees, about thirty in number, which have become exposed in this bed since its discovery, have been ransacked for such remains; and that while the majority have afforded some reward for the labour, some have been far more rich than others in their contents. It is also to be observed that owing to the mode of accumulation of the mass filling the trees, the bones are usually found scattered in every position, and those of different species intermingled; and that being often much more friable than the matrix, much labour is required for their development; while after all has been done, the result is a congeries of fragments. A few specimens only have been found, showing skeletons complete, or nearly so, and I shall endeavour to figure one or two of these by way of illustration in the present chapter.

The beds on a level with the top of the reptiliferous erect trees are arenaceous sandstones, with numerous erect Calamites. I have searched the surfaces of these beds in vain for bones or footprints of the reptiles which must have traversed them, and which, but for hollow erect trees," would apparently have left no trace of their existence. On a surface of similar character, sixty feet higher, and separated by three coals, with their accompaniments, and a very thick compact sandstone, I observed a series of footprints, which may be those of Dendrerpeton or Hylonomus.

A typical Carboniferous Microsaurian, Hylonomus Lyelli Restoration showing dermal armour and ornaments. Skeleton restored from measurements of the bones of the type specimen figured at the beginning of the chapter.