WERE LAID DOWN 



If this be true the seven-inch layer would be reduced to 

 less than one and a half inches, and a layer a foot in 

 thickness would require between 8000 and 9000 years. 

 The aggregate thickness of coal is frequently as much as 

 100 feet (when all the thicknesses of the seams are added 

 together), and sometimes as much as 250 feet. At the 

 foregoing rate of accumulation periods ranging from 

 1,000,000 to 2,500,000 years would be needed for the 

 accumulation of such thicknesses of coal. It must be 

 borne in mind that much depends on the rate of growth 

 of Carboniferous vegetation, which may have been, and 

 probably was, much more rapid than any we know out- 

 side tropical forests. On the other hand, we have been 

 speaking of the aggregate thickness of the coal beds 

 only. The greater part of the coal-bearing strata con- 

 sists of shale and sandstone with layers or seams of coal 

 like streaky bacon. Of the shale and sandstone there are 

 thousands of feet, even where the sediments are fine and 

 their accumulations therefore probably slow. For, as we 

 have said, this was a period of great change, in which 

 the forests were always sinking and rising again, being 

 submerged by lakes, being covered by the sea, and again 

 emerging as islands, to be overrun by vegetation. 



As sinks some sylvan scene in all its pride 

 Changed to lagoons of overflowing tide, 

 Assiduous labours Land to win again 

 Her leafy breadths, invaded by the main. 

 Down bring the rivers to the flooded shore 

 Cargoes of shale and silt that slow restore 

 The sunken glebes, till they again can hold 

 Thick ferny brakes, and forests as of old. 



(H. R. KNIPE.) 



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