nIr. LyelPs Sixth Lecture on Geology.
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on FOSSIL FOOTPRINTS.


HAVE been asked by several persons who heanl
my last lecture, upon the Origin OF Coal, if could
explain the difference between Coal and Anthra.
cite; aud as then had no time to touch upon this
subject, although my last ecr1re was prolonged
bevond the limit which l -;shed, VIII nov
speak of it in few words 1t tcertainly is good
questions; but several persons nave asked me
whether conceding thc vegetable origin OF coat, IL
may not he the dlfereaec IN Me uood when
causes the difference in the coal whether one
kind may not produce the Coal and another the
Anth:acitc. Now there is no doubt that, III the
strata of the Earth, there is some variety IN the
character e tho various Goals discovered, which
NAV I've. owing 10 a difference in the original text
ure and composition Of the different plants from
which they were formed. But this, nevertheless,
IS not the cause Of the difference between Anthra>
cite and Bitupinous Coal, as they have been pro-.
ducet by the same plants There is no doubt tha;
the Pala1, and other Monocotyledonous plants and
bamboos, reeds, &c. would give kind Of coal to
ccrtaia degree different from that produced by the
fir and other Dicotylcdons But as precisely the
same assembagc OF plants is found in the Anthra-
cite and Coul, it cannot be n this way that the
difference between these substances is caused
and the conclusion to which the geologist and
chemist have come is this that Anthracite has
once been Rituminous Coal, but has los, its btu
minous matter by it, escaping; that the volatile
part of it has escaped and the wood has becemc
gradually converted into coal by the loss ofits
ygen-vcgetables being composed of carbon, ox.yA
gen, and hydrogen. he vegetable matter losing
first its oxygen loses also in the combination
portion of its carbon forming carbonc acid
which escapes from the wood, often as "a pure
cas-as may be seen in bubbles which rise from
the bottom of pools of water: It is thas converted
into coal by the loss of its oxygen; and this
version /. gradual that there are found in the
Earth woods in every stage OF the change-botll in
that state when they are cullcd hgn,tes and when
they have become perfect coal. We lind. too, all
the intervening forms between wood and coal and
then all between coal and anthracite This is
caused again BY ,hc loss of the hydrogen which es
capes in combination with carbon, in the form Of
carburetted hydrogcH gas-tlle same substance that
are now burning here. You are aware that this
gas cannot be produced from anthracite because in
that the operation has already taken place. it man
utactuled entircyfron bitumnous coal This vul.
attic, nnammnble gas may be seen to escape from
rents in the Ear,ll-naturul rents from which this
carho hydrogen issucs; and if the coal below be
examined it will be found to be in process Of grad
lal change. But there is one remarkable fact Oh.
served in this country that, in the coal region of
Pennsylvania for exanple,--and this has been es-
pecially pointed out by Prof. RoDGEHs in his sur-
vey of Pennsylvania-the anthracite is found to be
purestin the disturbed part of the mountains
and it's half bituminous when you get into the re-
gions that have been slightly disturbed-n the
western part OF the State; and when you reach the
perfectly horizontal coal dstrict-that where there
has been no disturbance, no shatterng and tear
ing up of the mountains-there the coal is purely
bitumnous, not having lost its hydrogen. Some
have suggested that this is owing to the rending
and assuring of the rocks in the disturbed region
in which all.the volatile matter would have escaped
easily. OF this there is no certainty. But
the general fact is undoubed-tllat in proportion
to the disturbance, overthrow and bending of the
strata-some Of which have been folded back upon
thcmselves-do we find that the conversion into
anthracite from pure carboni most complete.


The next subject of which | shall treat is that of
Fossil Footsteps found in the formation which VIC
call the New Red Sandstone Its position in the
series is as follows


/. Chalk


2. Oolite.


3. New Red Sandstone.


A. Magnetism Limestone.


5. Coal.


s. Old Red Sandstone.


l. Silurian Group.