Ch. XXIV.] IN NOVA SCOTIA. 487 



trees (c and d), while at a greater height the trees / and g rest upon 

 a thin seam of coal (e), and above them is an underclay, supporting the 

 4-feet coal. 



If we now return to the tree first mentioned (fig. 540), we find the 

 diameter (a b) 14 inches at the top and 16 inches at the bottom, the 

 length of the trunk 5 feet 8 inches. The strata in the interior consist- 

 ed of a series entirely different from those on the outside. The lowest 

 of the three outer beds which it traversed consisted of purplish and 

 blue shale (c, fig. 540), 2 feet thick, above which was sandstone (d) 1 

 foot thick, and, above this, clay (e) 2 feet 8 inches. But in the interior 

 were nine distinct layers of different composition : at the bottom, first, 

 shale 4 inches, then sandstone 1 foot, then shale 4 inches, then sand- 

 stone 4 inches, then shale 11 inches, then clay (/) with nodules of 

 ironstone 2 inches, then pure clay 2 feet, then sandstone 3 inches, and, 

 lastly, clay 4 inches. Owing to the outward slope of the face of the 

 cliff, the section (fig. 540) 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 alter- 

 nating beds of shale and 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 

 sigillarian trunks support at different levels roots and stems of Catam- 

 ites ; the Catamites having begun to grow after the older Sigillarice 

 had been partially 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 com- 

 pared with their woody portion. The same difference of durability 

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

 me by Dr. 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 externally sound and fresh, although 

 consisting simpl} 7 of a hollow cylinder with all the wood decayed 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 Dr. Dawson to have Araucarian structure, so that some Coniferce 

 of the Coal period grew in the same swamps as Sigillarioe, just as now 



