DURATION OF THE COAL-FORMING AGES. 43 



and first ; but the beautiful and various forms of the dicotyledo- 

 nous plants, which constitute by far the greater part of the Flora 

 of the present day, were totally wanting in the swampy forests 

 of the carboniferous period, which, in spite of their amazing 

 luxuriance of growth, had but a monotonous and melancholy 

 character. No warm-blooded quadruped enjoyed their shade, 

 no bird enlivened them with his song. Their awful silence was 

 only interrupted by the tones of inanimate nature, the roaring 

 of the sea against the low beach, or the moaning of the wind in 

 their feathery fronds. But who knows whether spirits hovering 

 over their dreary expanse may not have whispered to each other 

 of the nobler creation for which they paved the way ! 



The great uniformity of climate which then reigned over the 

 globe caused at the same time a wonderful uniformity of vege- 

 tation in its various zones. In the eastern as in the western 

 hemisphere, between the tropics and beyond the Arctic circle, 

 wherever coal has been deposited the naturalist meets with the 

 same forms, often even with the same species of plant. 



The space of time required for the formation of the coal-fields 

 is as immeasurable as the countless millions of miles that sepa- 

 rate us from Sirius. 



We know by experience how thin the sheet of humus is 

 which the annual leaf-fall of our forests or turf-plants produces, 

 and how many decenniums must pass ere one single inch of solid 

 residuum is gained. But there are many coal-strata twenty to 

 thirty feet thick ; and if we consider besides the mighty pressure 

 of the superincumbent rocks which store them in the smallest 

 compass, we cannot possibly doubt that one such stratum must 

 have required thousands of years for its formation. Our wonder 

 increases when we reflect that, in many carboniferous basins no 

 less than a hundred thick and thin seams of coal alternate with 

 layers of sandstone and shale, so that the reckoning would swell 

 to millions, were we able to fathom the ages of their successive 

 growth. 



Thus, for instance, at Sheriff Hill, near Newcastle, we find eight 

 strata of coal of a joint thickness of thirty-three feet and a half, 

 but these are separated by intervening stone strata of an average 

 thickness of from forty to sixty feet, so that the entire thickness 

 of these coal measures amounts to 345 feet. 



But even these coal-bearing strata form but a small part of 



