VALLEY REGION; ORIGIN OF THE ROCKS. 145 
Tlustrations of all three of these cases will be piven in the 
special description of the valleys. 
It seems hardly necessary to state in so many words that 
the strata of our different Coal Fields as well as of the geo- 
logical formatiozs that underlie them, were from their very 
mode of origin continuous, and that their present separa- 
tion has come about through the foldings, faults, and denu- 
dations, which we have been describing. 
We might infer that after the strata had been thus brought 
up and added to the land area, their subsequent history 
would be merely a record of gradual degradation and level- 
ing down by erosion. But we have evidence in the lower 
part of the region shown on this map, that after this part of 
the State. had been elevated and undergone the changes 
mentioned and attained almost its present configuration, it 
was in part again submerged below the water level, and was 
overspread by the washings from that part which remained 
above the water. Only in this way could the great beds of 
sand, clay, and pebbles which cover so much of the area in 
the lower portion of the map, have been deposited upon the 
ridges and the valleys of the old land surface. This sub- 
mergence happened during the period termed by geologists 
the Cretaceous, which is comparatively modern as contrasted 
with the age of the formations above named. From the 
distribution of these beds we can see that the shore line 
during this time of partial submergence ran in a curve 
stretching from the northwestern part of the State to near 
the middle, at Columbus, Ga. To the west and south of 
that line the land sank below the water, while it remained 
above water to the east and north. 
And still later, almost in modern times, geologically speak- 
ing, when the dry land area of Alabama had attained its 
presentextent, and the surface had by long continued denuda- 
tion acquired almost its present configuration, our State was 
again below water, receiving deposits of pebbles, sand and 
mud, which in the upper part of the State have since been 
in great measure been washed away again, but patches of 
which still remain often upon the summits of the highest 
hills. In the lower half of the State these deposits have 
lu 
