294 THE BORDERLAND OF SCIENCE. 



miles.* Here no fewer than eighty seams of coal have 

 been counted (seventy-one having been exposed by the 

 action of the sea) ; but these seams are nowhere more 

 than five feet in thickness, and many are but a few inches 

 thick. Thus it is evident that the formation of coal 

 can have been in progress but for a short portion of 

 the time during which the great carboniferous series 

 of strata was in process of deposition. Throughout 

 by far the greater portion of that time other minerals 

 were being deposited. 



It is next to be noticed that under each coal-seam a 

 stratum of ancient soil exists, in which there are 

 commonly found the roots of ancient trees ; while 

 above the coal there is commonly a layer of shale or 

 sandstone, in which not unfrequently the trunks of 

 those trees are found either fallen or still in their 

 original position, and only partly converted into coal. 

 The bark remains, but is transmuted into coal ; the 

 hollow of the trunk, decaying long before the trunk 

 gave way, is represented by a cast in sandstone. Thus, 

 if we try to picture to ourselves the state of things 

 which existed when such a seam of coal first began to 

 be covered up by the next higher deposit, we see that 

 there must have been trees standing erect above a layer 



* The way in which this has been made known is worthy of notice. 

 In the Bay of Eundy the tides run to an enormous height. The tidal 

 wave can be seen when it is still thirty miles away, advancing with a 

 prodigious uproar, and rising sometimes to the height of more than a 

 hundred feet. These tremendous waves have not only produced a con- 

 tinuous section ten miles long, through the inclined strata, but by their 

 action they sweep away continually the whole face of the cliffs, and 

 bring into view fresh sections year after year. 



