412 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



I'his upper bench of the lower Pilot is a network of long straight 

 roots radiating from the stumps. David recognizes that the tufifs 

 must, have accumulated rapidly as, otherwise, the stems would have 

 rotted away. This roof forest is well shown on French Bay of 

 Lake Macquarie. The tree stems are chalcedony above the coal, but 

 in the coal they are a hydrocarbon. They are lo to 15 inches thick 

 and are about 5 yards apart. Drops of resinous matter, distilled 

 from the broken branches, are present in tuff surrounding the stems, 

 such as one finds in recent tuffs within the Andes region. The lower 

 bench of the bed has numerous stems and vertical roots, which David 

 conceives may be the remains of another fossil forest. The under 

 clays of both Pilot seams have abundant Vertehraria, while some 

 partings have Vertehraria and Sporangia. 



The Burwood seam, 13 feet thick inclusive of partings, gives evi- 

 dence of contemporaneous erosion before or during deposition of 

 the overlying shale. The conglomerate above has rounded pebbles 

 of coal, one to three inches diameter. David is inclined to believe 

 that these came from the Burwood seam, though he grants that the 

 source may have been one of the Greta seams. . They are proof that 

 when the conglomerate was deposited coal, already hard, existed. 

 Vertehraria abounds in underclays of coals in the lower division and 

 stumps, in situ, were seen in the roof of several seams. A gravel 

 bank, 70 feet thick and one fourth to one half mile wide, marks the 

 course of an ancient erosion. The vertical stems, in all cases, are 

 conifers. 



In summing up the facts, David state that the floor of each seam 

 contains abundance of Vertehraria (the root of Glossopteris), while 

 the roof shows more or less well preserved stumps of in situ trees. 

 The lower part of stumps and roots, where they form part of the 

 coal seam, still retain a large proportion of the original carbon and 

 only the upper part has become slightly silicified. But the tree 

 stump, where extending a few feet above the coal seam, is com- 

 pletely silicified, changed into chalcedony, but the minute tissue is 

 usually preserved. Where the woody portions are replaced with 

 carbonate of iron, retaining the woody structure, the bark, one or 

 two inches thick, has become brittle, bright bituminous coal. This 

 leads him to suggest that the bright laminae of the coal were made 



