Editorial CoDimenf. 335 
the above reasons will bind us forever to tlie first theory. Not 
only is it a good reason in itself, at least to the extent of ex- 
cluding driftage as a valid explanation, but Gresley himself 
makes no attempt to render comprehensible that which "ap- 
pears to be totally beyond our comprehension." Until some 
one can show us, in estuary or delta somewhere, a raft of vege- 
tation accumulated by drifting which is pure enough to form a 
good seam of coal, we need not strain our faculties in the at- 
tempt to compreheud how it could get there in such a state of 
purity and freedom from intermixture with earthy sediments. 
Gresley states that his "principal object is to bring forward 
evidence in opposition to the view now generally accepted that 
coal seams are formed from vegetation Avhich grew on the spot;" 
yet he liesitates, or appears to hesitate, about adopting the 
driftage theory. What would he have? Is there a third al- 
ternative? He says in conclusion that "what evidence we do 
possess decidedly favors a drift or at all events an aqueous ori- 
gin." Whatever he means by "aqueous origin" makes all 
the difference l)etween his theory and that of growth 
in situ. When he shall tell us more clearly just what he 
means we shall probably find no difficulty in agreeing with 
him, for the general belief is that coal is of aqueous, i. e.y 
swamp origin. 
The meaning of "growth in situ''' perhaps needs explanation 
also. Gresley interprets it with literal exactness, as if each cu- 
bic foot of coal was produced upon that identical square foot 
of surface. The body of his paper is devoted to disproving the 
proposition that coal plants grew from the uuderclay up 
through the coal seam and thus produced the latter! Some 
careless reader of carelessly written elementary text-books may 
entertain such a notion, but no practical geologist ever did. 
What is meant by growth in situ as opposed to driftage may 
be illustrated by the actual conditions in existing swamps. The 
products of vegetable growth, leaves, twigs, spores, pollen, &c., 
not only fall where they grew but are carried by winds over the 
adjacent lagoons where nothing grows. Lesquereux found 
the bottom of Drummond lake, in the Dismal swamp, covered 
'with the same layer of vegetable matter which fills the sur- 
rounding swamp. So the open lagoons of swamps in the Car- 
boniferous age received their share of vegetable debris, and 
