322 JESSE E, HYDE 
index of the amount of compression which has taken place in the 
coal. 
However, the actual original thickness of the organic mud, and 
the exact amount of compression it has suffered, are only incidental 
to the subject under consideration, and are not at all essential to 
the interpretation of the associated structures. 
POCKETS OF COAL NOT ACCUMULATED SIMULTANEOUSLY BUT 
SUCCESSIVELY 
When one of the coal pockets splits into a number of thin layers, 
the layers spread out vertically through several feet of sandstones. 
These may or may not reunite to form the next adjoining coal 
pocket. More commonly they do not. The topmost coal parting 
on the side toward the source of the sands commonly rises with the 
rise of the bedding planes entirely above the coal pockets in that 
direction. On the other hand, the topmost parting on the side 
away from the source of the sands usually passes into the middle 
of the next pocket in that direction, or into its lower part or even 
entirely below the lowest stringer which comes from it. This is 
due to the gentle inclination of the sandstones. 
This signifies an unusual method for the accumulation of the 
coal, if it is correctly interpreted. If the topmost and bottom- 
most stringers from two coal pockets are continuous from one to 
the other, no matter how far vertically they may diverge in the 
intervening sandstones, they are held to have been deposited 
simultaneously. On the other hand, if the top of one passes into 
the middle of the next one, the upper half of the latter is held to 
have accumulated after the former had ceased to form, or if the 
top stringer from one passes entirely beneath the bottom of the 
next one, the latter is held to have been wholly deposited subsequent 
to the former. These are the premises on which the conclusions 
rest. 
When all of the coal pockets (nine in number) are considered in 
that portion of the cut where outcrops are entirely unobstructed 
and where the source of the material is persistently from the south- 
west, it is apparent that the one at the southwest end is the oldest, 
that is, the one nearest the source of the inclined sands. Further- 
