1853.] DAWSON — COAL-MEASURES, NOVA SCOTIA. 19 



less than thirteen distinct forest-surfaces, marked by underclays or 

 erect trees, and five periods of submergence indicated by beds with 

 Modiola, &c., and three of them, at least, of very long duration. It 

 will be observed that, in three instances, the order of succession is 

 underclay — coal — bituminous limestone. This arrangement, so com- 

 mon in other parts of the section, seems to show a connection other 

 than accidental between the long periods of terrestrial repose required 

 for the growth of coal, and those of quiet submergence necessary for 

 the growth of Modiola-beds. Perhaps the submerged coal-swamp 

 was the most fitting habitat for Modiola and its associates ; and 

 these sunken swamp-areas may have been so protected by thick mar- 

 gins of jungle as to resist for a long time the influx of turbid waters. 

 In ascendmg through Group XIII., the first object of interest is 

 a band of bituminous limestone with Modiola, Coprolites, and Cypris, 

 which forms the roof of one coal and the imderclay of another, evincing 

 important changes of level with scarcely any sedimentary deposi- 

 tion. Above the upper coal, however, we have an erect plant, only 

 4 inches in diameter, surrounded by arenaceous shale, and, in the 

 finer clay surrounding its base, Poacites with attached Spirorbis, 

 which probably, like some of its modern congeners, could grow 

 rapidly, and with equal facility, either on drifting or stationary plants. 

 Still higher in this group, and immediately above a thick bed of 

 bituminous limestone and Modiola-shale, is a very curious association 

 of erect plants. An erect tree, converted into coal, springs from the 

 surface of the shale, and passes through 14 feet of sandstone and 

 shale. Apparently from the same level there rises an erect ribbed 

 tree, probably a Sigillai'ia, in the state of a stony cast, which, how- 

 ever, extends only to the top of the sandstone. In the sandstone, 

 and rooted about a foot above the base of the erect trees, are a num- 

 ber of erect Catamites. In this case the forest-soil has been covered 

 by about a foot of argillaceous sand, on which a brake of Calamites 

 sprung up. Further accumulations of sand buried them, and covered 

 the trunks of the trees to the depth of 8 feet. By this time the 

 Sigillaria was quite decayed, and its bark became a hollow cylinder, 

 reaching only to the surface of the sand, and ultimately filled with 

 it. The other tree still stood above the surface, until 6 feet of mud 

 were deposited, when, its top being broken off, it also completely 

 disappeared beneath the accumulating sediment ; and being softened 

 and crushed by the lateral pressure of the surrounding mass, it was 

 finally converted into an irregular coaly pillar, retaining no distinct 

 traces either of the external form or internal structure of the original 

 plant. The structure of similar trees, to be noticed further on, ren- 

 ders it likely that this coaly tree is the remains of one of the Arau- 

 carian Conifers, which, it appears, flourished in the coal-swamps 

 in company with the Sigillaria. The surface of the clay which 

 buried this remarkable tree became itself an underclay or soil ; and in 

 the sandstone resting upon it were found casts of two erect trees, one 

 of them 5 feet in height, and a Sigillaria with distinctly marked 

 leaf-scars. The tops of these trees have been entirely removed, 

 and their hollow stems filled with sand, before the deposition of a 



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