.90 MONOGRAPH OF DTTEA DEN. 



and their remains to be afterwards enclosed in the shales and 

 breccias of the system. New shores likewise were to be formed, 

 new basins to be constructed, new boundary lines to be cast up 

 from below, and dry lands submerged from above, and a 

 mechanism of forces arranged underneath the crust whereby 

 to admit the successive deposition of marine, estuary, and 

 fresh-water detritus of which the coal-measures all over the 

 earth are so marvellously composed. Here is presented the 

 evidence of vast changes of physical condition and oscillations 

 of level, showing that as frequently as the successive strata 

 were deposited, so frequently did the seas swarm with their 

 teeming inhabitants, and the lands wave under a dense vegeta- 

 tion ; while as many times were there the repeated alternations 

 of lakes, estuaries, lagoons, and seas of deeper and sometimes 

 of shallower bottoms. 



The peculiarity of this flora is the great number of the vas- 

 cular cryptogamic plants, which amount to two-thirds of the 

 species of vegetables discovered in the carboniferous deposits. 

 With these are associated a few palms, coniferse, cycadese, and 

 some species of plants allied to the cactese and euphorbiacse. 

 The ferns are the most prevailing types, large arborescent 

 kinds, of which several hundred, belonging to many genera, 

 have been determined. Many of the strata of shale are entirely 

 made up of carbonized fern leaves and stems closely pressed 

 together. The roof of a coal mine, when newly exposed, often 

 presents the most wonderful appearance, from the amazing 

 abundance of these most graceful of all plants, and the infinite 

 variety of leaves, branches, and stems that are displayed, some- 

 times in relief, sometimes impressed on the dark shining surface. 

 When the shale or stone is of a light colour, the contrast of the 

 black carbonized foliage renders the effect perfectly enchanting, 

 rivalling ever^^thing in the shape of sculpture, mosaic intaglio 

 tracery, or all that was collected of art in the most admired 

 compartment of the Crystal Palace. But most remarkable of 

 all, the plants of the coal-measures, from Greenland to Aus- 



