THE CARBONIFEROUS AGE. 115 



the once fertile plains of the coal formation again 

 under the waters; and shifting sand-banks and 

 muddy tides engulfed and buried the remains of the 

 old forests, and heaped on them a mass of sediment, 

 which, like the weights of a botanical press, flattened 

 and compressed the vegetable debris preserved in the 

 leaves of the coal formation strata. Then came on 

 that strange and terrible Permian period, which, like 

 the more modern boulder-formation, marked the death 

 of one age and the birth of another. 



The succession just sketched is the normal one; 

 but the terms in which it has been described show 

 that it cannot be universal. There are many places 

 in which the whole thickness of the Carboniferous is 

 filled with fossils of the land, and of estuaries and 

 creeks. There are places, on the other hand, where 

 the deep sea appears to have continued during the 

 whole period. In America this is seen on the grand- 

 est scale in the absence of the marine members 

 along the western slopes of the Appalachians, and the 

 almost exclusive prevalence of marine beds in the far 

 west, where the great Carboniferous Mediterranean of 

 America spread itself, and continued uninterruptedly 

 into the succeeding Permian period. 



In our survey of the Carboniferous age, though 

 there are peculiarities in the life of its older, middle, 

 and newer divisions, we may take the great coal 

 measures of the middle portion as the type of the 

 land life of the period, and the great limestones of 

 the lower portion as that of the marine life ; and as 



