1853.] DAWSON — COAL-MEASURES, NOVA SCOTIA. 31 



cast must result. (2.) The interior of the cyhnder of bark has often 

 been smeared with clay before a cast was taken, and this clay either 

 comes away with the bark, or falls off when weathered, taking with it 

 the finer parts of the cast. (3.) The portion preserved in an erect 

 position is generally only a few feet of the base of the trunk, where 

 the markings were probably nearly obliterated by growth. (4.) In 

 one instance rootlets oi Stigmaria were observed to pass downward 

 between the bark and the matter filling the interior, and leaving ver- 

 micular impressions of their own form over the whole surface. When 

 all these causes are allowed for, it will not appear remarkable that 

 few erect trees retain their surface-markings, and that these should 

 generally be of the broad-ribbed and strongly marked species. 



The dome-shaped fossil in the centre of Stigmaria, as described 

 by Lindley and Hutton, and a similar body found at Sydney by 

 Mr. Brown have occasioned doubt as to the true nature oi Stigmaria. 

 Such appearances may have been produced in the following manner. 

 The trunks of Sigillaria usually expand rapidly toward the base, and 

 if broken off near the soil, there would be a tendency in the bark, 

 during decay of the wood, to fall in toward the centre. This would 

 be much facilitated by the circumstance that the bark of Sigillaria 

 was weak along the furrows, and hence tended to split into strips. 

 Such strips, each with a row of leaf-scars, are found among the detached 

 fossils on the Joggins shore. In the falling in of the bark, they 

 would readily overlap each other and form a continuous coaly 

 surface, leaving on the internal cast impressions of some of the leaf- 

 scars, if any existed so near the root. Farther, the abrupt breaking 

 off of a cylinder of bark projecting above the surface would crush 

 together the sides of the imbedded portion, leaving only an open slit 

 at top. This is well seen in the broken tops of erect Calamites*, and 

 a curious instance of a similar deceptive appearance is presented by 

 erect Calamites in this section, which, when imperfectly filled with 

 sediment, assume either the appearance of a vertical row of lenticular 

 bodies strung on a thin irregular string, or that represented in fig. 15. 



The tendency of Sigillarice. to have four main roots di\ading 

 regularly at equal distances has been noticed by Messrs. Binney and 

 Brown. It is illustrated by several erect trunks in this section 

 (figs. 6a & 8, MS.), and still better by the remains of the erect trees 

 found at Port Hood. Fig. 1, Port Hood, ms., represents a large 

 erect stump with its four main roots. Fig. 4, PortHood, ms., represents 

 the markings on this root. Fig. 4, p. 23, represents the impression 

 of another large stump in the sandstone. Fig. 5, Port Hood, ms., re- 

 presents the markings of another species of Stigmaria found in the 

 same bed. Accidental deviations from this singularly regular division 

 of the roots are sometimes met vrith. In a collection at the Joggins, 

 there is a small stump from the roof of the coal seam, vdth two large 

 and two small roots, as if it had grown on the slope of a bank or edge 

 of a channel. It is also common to find, especially in large trunks, 

 instead of four roots, four great lobes giving origin to eight roots. 

 The whole of this arrangement, as well as the peculiar structure of 

 * Quart. Jom-n. Geol. Soc. vol. vii. p. 196. 



