54 
HAROLD’S DISCUSSIONS. 
The logs were so pressed together that they made a 
layer of coal only about an inch in thickness. He 
found that these tree-stumps had their roots embedded 
in a layer of shale, which was mud or clay during 
the growth of the tree, and had been changed to 
rock beneath the coal. 
I have read other descriptions of the rocks of the 
Carboniferous age, and all agree that beneath the coal- 
seam there is always a layer of shale, and that in this 
shale are the roots of trees. Sometimes the seams 
have shifted from a horizontal position ; in such cases 
Fig. 31. —Section of peat-bog. A, remnant of pond; B, B, living 
sphagnum; C, C, peaty mass from disintegration of surface 
layer of plants; D, D, solid part of swamp with trees. (After 
Shaler.) 
the stumps are no longer upright, but oblique, show¬ 
ing that the seam was tilted after the coal was 
formed. 
All these facts will suggest to you that coal had 
something to do with vegetation, and is probably 
made from it, but how ? At the present time, in the 
bottom of many peat-bogs, there are several feet of 
decayed vegetation, so well packed together that it 
forms a kind of poor grade of coal called peat. Be¬ 
neath this is a layer of clay, in which are embedded 
