96 PAL2EOZOIC TIME. [CHAP. VI. 



while the occasional occurrence of a marine band indicates 

 a time when the downward movement was more rapid than 

 usual, causing the waters of the open sea to overflow the 

 wide alluvial levels. Lastly, from the overlap of the Coal- 

 measures, and from the wide extension which individual 

 coal-seams attain in the Middle Coal-measures, we may 

 infer that the area of the marshy flats on which the coal- 

 plants flourished was being continually increased at the 

 expense of the higher and drier inland districts which they 

 surrounded. 



We know what a wide extension the Coal-measures had 

 over the British area, and that what are now separate 

 basins or coalfields were originally connected and con- 

 tinuous areas. But this great development of Coal-mea- 

 sures is by no means peculiar to Britain ; coalfields are 

 found in many parts of the Continent, notably in France, 

 Belgium, Germany, and Russia, everywhere presenting a 

 similar aspect and a similar succession of measures, making 

 it certain that they belonged to one natural province or 

 geographical area. 



We must conclude, therefore, that over a large part of 

 what is now Europe there existed vast tracts of alluvial 

 land but little above the sea-level, the conterminous deltas, 

 in fact, of the rivers which drained the surrounding land, 

 just as Holland is the conterminous delta of the Rhine, 

 Meuse, and other rivers. It is as if an area as large, or 

 larger, than that covered by the Mediterranean Sea, were 

 slowly silted up and converted into one enormous swamp. 

 To bring about such a result there must have been many 

 rivers of large size emptying themselves into this sea, 

 rivers comparable to the largest which now exist in the 

 world, and for the supply of such rivers the surrounding 

 continents must have possessed mountain ranges compar- 

 able to those of America and Central Europe, and must 

 have been watered, by a copious rainfall. 



