
164 B. N. A. BOUNDARY COMMISSION. 



= 
matter, without coarse grains, and not more in amount than may have 
been contained in the substance of the original vegetable materials. 
Though some of the lignites may have been formed from accumulations = 
of drift-wood in shallow water, it is difficult to understand how such 
collection could go on for long periods, without the contemporaneous 
deposit of sandy or muddy matters, which would have been suspended in — 
waters moving with sufficient force to convey the wood. It would also 
appear difficult under this theory, to explain the regular and even super- 
position of the sandy and clayey beds, which overlie the lignites, and the 
fact that these do not send extensions downward into them, as they must 
have done if formed above a tangled mass of trunks and branchesof trees. _ 
It seems likely, therefore,—though layers like true root-beds were only 
observed in one or two instances to underlie the lignites—that at 
least the majority of these beds were produced by the growth and 
partial decay of trees, and also perhaps of peaty matter from swamp 
mosses, in the positions which they now occupy. Their method of for- 
mation would, therefore, agree with that already proved for coals of the 
true Carboniferous formation. This is rendered more probable by the 
circumstance that lignite beds are sometimes immediately covered by beds 
holding leaves of trees, ferns, and grasses, a fact which has been noted 
by Dr. Hayden and others with regard to those further south, and — 
which is also found to obtain with coal beds of the Carboniferous period. 
Some of the more impure beds, indeed, seem still to show evidence of 
having been formed from accumulations resembling those of a peat-bog, 
in which occasional logs of wood have been enclosed. A great part of 
such a bed is soft and structureless, but it holds irregular masses of hard 
jet-like material, with conchoidal fracture, and evident remains of woody 
structure. As already stated, also, some of the more impure lignites 
seen in the further western portion of the formation, seem compatible 
with the explanation of formation from drift-wood. 
Combustion of Lignite Beds. 
386. In connection with the Lignite Tertiary, the phenomena of the 
combustion of lignite beds over great areas, and the metamorphosis of 
rocks, and features impressed on the country by it, is. a subject of in- 
terest and importance. In no part of the world does this destruction of 
mineral fuels seem to have occurred on so vast a scale, as in the central 
plateau of this continent. The appearances produced by this action were 
met with in the vicinity of the forty-ninth parallel, at the very eastern 

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