3T4 



PALAEOZOIC SYSTEM OF ROCKS. 



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they lay where they fell, but it is incompatible with driftage by rapid 

 currents to long distances, c. The position of these perfect specimens 

 only on the upper part of the seam, as would be the case with the last 

 fallen leaves, instead of mixed throughout the seam, as would be the 

 case with drifted matter, d. The presence of stumps with their spread- 

 ing roots penetrating the under-clay exactly as they greiv. This is not 

 an occasional phenomenon, but is found in the under-clay of nearly 

 every coal-seam- In South Wales there are 100 seams of coal, every 

 one of which is underlaid by clay crowded with roots and sometimes 

 with stumps. In Nova Scotia there are seventy-six seams, twenty of 

 which have erect stumps standing in their original position with spread- 

 ing roots still penetrating the under-clay. The other seams have each 

 its under-clay filled with stigmaria-roots. Besides these seams there are 

 many dark bands (dirt-beds) indicating old forest-grounds. 



The following section (Fig. 515) shows some of these seams and 

 dirt-beds or forest-grounds, with penetrating roots and erect trunks. 

 Fig. 516 shows an area of about one quarter acre of surface of the 



under-clay of an English 

 coal-seam in which there 

 are seventy-three stumps 

 in situ. This last evi- 

 dence (d) is demonstra- 

 tive. Beneath every coal- 

 seam there is a fossil soil — 

 an ancient forest-ground. 

 Recapitulation. — We 

 may sum up the evidence, 

 and at the same time make 

 it clearer, by describing a 

 section of a peat-bog, and comparing with a coal-seam. In such a sec- 

 tion we have always an under-clay, on which accumulated the moisture, 

 and on which grew the original trees of the locality. This under-clay 

 is often full of roots and stumps of the original growth. Above this is 

 a fine, structureless, carbonaceous mass, corresponding to the coal- 

 seam. On this are the last-fallen leaves, not yet disorganized, and the 

 still-growing vegetation. Now, imagine this overwhelmed and buried 

 by mud or sand, the whole subjected to powerful pressure, and a slow 

 subsequent process of bituminization ; and we have a complete repro- 

 duction of the phenomena of a coal-seam with its accompanying under- 

 clay filled with roots, and its black shale filled with leaf and branch 

 impressions. 



2. Coal has been accumulated at the mouths of rivers, and therefore 

 in localities subject to floods by the river and incursions by the sea. It 

 is otherwise impossible to account for the clays and sands (often inclos- 



Fig. 515.— Erect Fossil Trees, Coal -Measures, Nova Scotia. 



