Ch. XXIV.] COAL — FOSSIL FORESTS OF NOVA SCOTIA. 879 



Owing to the outward slope of the face of the cliff, the section (fig. 493) 

 was not exactly perpendicular to the axis of the tree ; and hence, probably, 

 the apparent sudden termination at the base without a stump and roots. 



In this example the layers of matter in the inside of the tree are more 

 numerous than those without ; but it is more common in the coal- 

 measures of all countries to find a cylinder of pure sandstone, — the cast 

 of the interior of a tree, intersecting a great many alternating beds of 

 shale aud sandstone, which originally enveloped the trunk as it stood 

 erect in the water. Such a want of correspondence in the materials 

 outside and inside, is just what we might expect if we reflect on the 

 difference of time at which the deposition of sediment will take place in 

 the two cases ; the imbedding of the tree having gone on for many 

 years before its decay had made much progress. 



In many places distinct proof is seen that the enveloping strata took 

 years to accumulate, for some of the sandstones surrounding erect sigilla- 

 rian trunks support at different levels roots and stems of Calamites ; the 

 Catamites having begun to grow after the older Sigillariai had been par- 

 tially buried. 



The general absence of structure in the interior of the large fossil 

 trees of the Coal implies the very durable nature of their bark, as 

 compared with their woody portion. The same difference of dura- 

 bility of bark and wood exists in modern trees, and was first pointed 

 out to me by Mr. Dawson, in the forests of Nova Scotia, where the 

 Canoe Birch (Betula papyracea) has such tough bark that it may 

 sometimes be seen in the swamps looking t externally sound and fresh, 

 although consisting simply of a hollow cylinder with all the wood de- 

 cayed and gone. In such cases the submerged portion is sometimes 

 found filled with mud. 



One of the erect fossil trees of the South Joggins has been shown by 

 Mr. Dawson to have Araucarian structure, so that some Coniferw of the 

 Coal period grew in the same swamps as Sigillariai, just as now the 

 deciduous Cypress {Taxodium distichum) abounds in the marshes of 

 Louisiana, even to the edge of the sea. 



When the carboniferous forests sank below high-water mark a spe- 

 cies of Spirorbis or Serpula (fig. 498) attached itself to the outside 

 of the stumps and stems of the erect trees, adhering occasionally 

 even to the interior of the bark, — another proof that the process of 

 envelopment was very gradual. These hollow upright trees, covered 

 with innumerable marine annelids, reminded me of a " cane-brake," 

 as it is commonly called, consisting of tall reeds of Arundinaria 

 macrosperma, which I saw, in 1846, at the Balize, or extremity of the 

 delta of the Mississippi. Although these reeds are freshwater plants, 

 they were covered with barnacles, having been killed by au incursion 

 of salt water over an extent of many acres, where the sea had for 

 a season usurped a space previously gained from it by the river. 

 Yet the dead reeds, in spite of this change, remained standing in the 

 soft mud, showing how easily the Sic/Maria?, hollow as they were 



