KXl'LANATION OF JOGGINS SECTION. 197 



concealed under the beach. It was filled with sandstone to the height 

 of" seven inches above the level of the sandstone without, indicating 

 that this bed must have suffered from denudation, after having contri- 

 buted materials toward the filling of the stump. It is probable that 

 the sand within the bark was originally lower than that without. If 

 so, the sandstone may have lost much more than seven inches ; and of 

 this, but for the presence of this stump, there would have been no 

 evidence. The neighbouring tree, though rooted at the same level, 

 was brought by the dip of the beds to a sufficient height to allow its 

 roots to be seen. It was originally of the same height with the other, 

 but the upper part had been removed. In this stump we see that 

 while the sandstone within has extended higher than that without, it 

 has also descended lower, though not quite to the bottom, this being 

 filled with clay. We thus find that after the tree became hollow, and 

 while its top continued to stand at least three feet above the surface, 

 it was partly filled with a deposit from muddy water. The mud 

 within was, however, much lower than that without when the sand 

 began to be deposited, and filled the greater part of the stump. The 

 roots of this tree had Stigmaria markings, and the rootlets could be 

 seen penetrating the shale beneath. Portions of the surface of the 

 trunk showed the markings of a broad-ribbed Sigillaria, with oval 

 leaf-scars on the ligneous surface. The roots descend somewhat 

 rapidly into the clay, and perhaps even reach the coaly layer below. 

 The overlying shales bend downward into the upper part of these 

 stumps, indicating that the material within was more compressible 

 than that without. Perhaps this is due to the compression of woody 

 matter remaining in the bottom of the cavity left by the decay of the 

 trunk. The circumstances in which these stumps were preserved 

 strikingly illustrate the strength and durability of the bark o( Sigillaria. 

 Above this bed there are about thirty feet of shales, with ironstone 

 bands and sandstones, including a few thin layers of coal, and appa- 

 rently several underclays ; but the coal railway and pier prevent them 

 from being well seen. On these rests the main coal or " King's Vein " 

 (Coal-group 7). The main coal and a layer of clay six inches thick 

 overlying it, have supported a forest of Sigillarice, some of which 

 remain as erect stumps, others are prostrate. Very fine specimens 

 have been extracted from this bed in Avorking the coal. Their surfaces 

 are often covered with Spirorbis. This forest was buried under eight 

 feet of sand and clay; and from the surface of the latter sjjrang an 

 erect tree, which was observed to extend upward to the height of 

 fifteen feet, and was then abruptly broken off. The rocks enclosing it 

 are sandstone and arenaceous shale. (Fig. 10.) This tree, like one 



