THE CARBONIFEROUS PERIOD. 83 
upheaval in the neighborhood would disturb the 
equilibrium of the waters, causing them to over- 
flow and pour over the surface of the country, 
dius inundating the marshes anew. 
That such was the case we can hardly doubt, 
after the facts revealed by recent investigations 
of the Carboniferous deposits. In some of the 
deeper coal-beds there is a regular alternation 
between layers of coal and layers of sand or clay ; 
in certain localities, as many as ten, twelve, and 
even fifteen coal-beds have been found alternat- 
ing with as many deposits of clay or mud or 
sand ; and in some instances, where the trunks 
of the trees are hollow and have been left stand- 
ing erect, they are filled to the brim, or to the 
height of the next layer of deposits, with the 
materials that have been swept over them. Upon 
this set of deposits comes a new bed of coal with 
the remains of a new forest, and above this again 
a layer of materials left by a second freshet, and 
so on through a number of alternate strata. It 
is evident from these facts that there has been a 
succession of forests, one above another, but that 
in the intervals of their growth great floods have 
poured over the marshes, bringing with them all 
kinds of loose materials, such as sand, pebbles, 
clay, mud, lime, etc., which, as the freshets sub- 
sided, settled down over the coal, filling not only 
the spaces between such trees as remained stand- 
