410 



THE CARBONIFEROUS SYSTEM. 



doubled up. Some beds also seem to contain one species of plant 

 only, all others being excluded ; of this we have a striking example 

 in the argillaceous shale (No. 60) : in the top of this bed, through a 

 thickness of three inches, we find Asterophyllites foliosa, piled up 

 layer above layer, from the base of the cliff to the crop of the bed— 

 a distance of '200 feet — clearly proving that these plants grew on the 

 spot." This description may give the reader some idea of the abun- 

 dance and perfection of the fossil vegetatiun preserved in the Sydney 

 Coal measures. As already stated also, a bed of shale in the Sydney 

 section has afforded the finest example yet known of carboniferous rain- 

 marks. These occur in a bed at the top of one of those bands in which 

 the sandstones are rippled and fossils rare. At some distance below it 

 there are mussel shales, and ten feet above a stigmaria underclay and 

 coal. These marks then were preserved in beds formed during the 

 transition from aquatic to terrestrial conditions, by the silting up of a 

 lagoon or creek, and most probably on a bed daily left dry at low tide. 



In a previous chapter mention was made of the curious footprints 

 called Rusichnites, as occurring in the Lower Carboniferous. In the 

 Cape Breton Coal-field an interesting species occurs in the Coal meas- 

 ures (Fig. 157). The specimen from which the figure was taken 

 was kindly presented to me by R. Brown, Esq. 



Fig. 157. — Rusichnites Acadicus — Dawson 



Each impression consists of the casts of contiguous rounded furrows, 

 each about one-eighth of an inch in breadth, and crossed by curved 



