/S The American Geologist. February, i899 
not each individual layer or band of shale represent the earthy 
matter carried with the vegetation into the lake or sea, but 
which became disengaged from the latter by reason of its 
capacity for remaining longest in suspension in the water? 
If this be a true explanation of the phenomenon of these thin 
sheets of mud, there is some reason for supposing that these 
mud-layers were really "old soils" in which the coal plants 
grevV. But in this case if the above mentioned mode of their 
deposition is accepted, we have the "old soils" on top of the 
plant-remains they produced; and yet only "soils" in the sense 
that their ingredients formerly existed as soil upon the surface 
far away from their present resting place. Of course this 
hypothesis does not deny the existence of aquatic plants 
(algse. etc.,) in the lake or sea. It does seem to demand periodic 
floods, otherwise why not an unbroken flow or transportation 
of vegetable remains? It cannot, I think, be denied that this 
idea of the origin of the slaty layers in the coal furnishes a very 
satisfactory explanation of all the more important physical, 
stratigraphical and paleontological conditions, contents and 
aspects of the "Pittsburg" seam, which may be summarized 
thus : 
I. Stratification. 2. Lamination. 3. Marked alter- 
nations of vegetable with mineral sediments, etc. 4. Uni- 
formity of thickness of every individual la3^er, bed, or stratum. 
(Local irregularities of deposition proving the rule.) 5. 
Transported foreign pebbles or boulders. 6. Absence of 
Stigmaria. 7. Fish, mollusks, crustaceans, etc. 8. Vast 
areal extent covered by existing layers, (to say nothing of 
the probable original area involved). 9. The common ming- 
ling-ground or resting-place for vegetable remains of land 
and water forms, no matter how large or how small, from 
trunks of trees to pollen grains. 10. Agrees with the idea 
or theory of gentle and uniform subsidence over the whole 
coal-forming expanse, as opposed to that requiring repeat- 
ed elevations followed by subsidences — the see-saw theory. 
II. The existence of myriads of micro-organisms working 
molecular and chemical changes in the vegetable products 
and residues. 12. Ash of coal. 
If we do not regard the phenomena of this coal-bed in the 
light of the above suggestions, we come back again to the old 
