Geology. 291 
generally no thicker than the »,th part of an inch, alternate some- 
times with equally thin layers or lamine of compact coal, the question 
arises how could such thin layers be exposed to atmospheric influence 
while the intermediate laminz were transformed to solid coal by immer- 
sion? The supposition that the mineral charcoal represents the wood 
cies predominant in the shales overlaying the coal. Thus one bed (No. 
1B Coal) has, especially in its charcoal, blades of Lepidostrobus and leaves 
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the assertion of some authors—that Stigmaria is not found in the coal or 
es overlaying it is without any foundation whatever. Some 
coal have been formed by Stigmaria only. Whole strata of 
black laminated roof-shales contain only remains of Stigmaria. 
either the form or the size of the scalariform vessels can be admitted 
48 a generic character; the form of the perforations varies on the same 
vessel passing from round to oval, to equilateral and to true scalariform 
shape by gradual and inappreciable transitions. The size of the vessels 
Varies according to the size of the same plant. : 
e of the most interesting conclusions reached by Prof. Dawson is 
that the small cylindrical filaments, resembling black threads, so abundant 
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he vessels figured 8 to 12 of pl. 18, apparentl belong to some spe- 
cles of Stiymaria, especially to S. ficoides (compare Corda’s Beytrage, tab. 
wineral charcoal is a proof of my assertion, that Stigmaria enters largely 
into the formation of the coal. 
It is scarcely possible now to refer the genus Sigillaria to Cycadea or 
to the Conifere. Neither the internal structure nor what we know of the 
&xternal forms of species of this genus, the leaves, the fruits, &c., can show 
such an analogy, ot 
= Prof. Dawson .can not with certainty affirm the presence of tissue of 
true Conifers in the coal. This agrees perfectly with the result of ten 
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~The writer does not think that the coal measures of Nova Scotia Laie 
eg exhibition of the general formation of the coal. The coalfields of 
Mov. tty bear testimony to such continual disturbance by the repeated 
of the surface, repeated overflows, sudden invasions of littoral 
» 
