J. G. Canc ereematian of Coail-seams. 309 
Perhaps the truth in this case, as in many others, may be that 
similar results have been attained in a variety of ways, and that, 
instead of there having been but one mode of formation of coal- 
seams, there have probably been many. 
We might briefly consider some of these at this point. The 
formation of coal simply requires that a certain quantity of pure 
vegetable matter should be left at any given spot under conditions 
that insure its conversion before its chief constituents shall have 
passed into the inorganic condition. These results may be brought 
about in a variety of ways. Inland, for example, coal or its repre- 
sentative, lignite, may be formed through the burial of peat beneath 
the alluvium of lakes or of rivers. In marine areas it may arise 
through the sedimentation of inland peat whose constituents have 
been re-sorted and drifted out to sea. The submergence and sub- 
sequent burial of maritime beds of peat in sit may, under suitable 
conditions, give rise in another way to beds of coal. The entomb- 
ment of masses of drift-timber that have floated seawards must, 
again, largely contribute to the same result. Marine vegetation 
must occasionally play an important part in the formation of deposits 
of carbonaceous matter on the sea-bottom.’ Then there is the im- 
portant factor of the growth, decay, and entombment on the spot, of 
lagoon vegetation, originating in an area where deltas are subsiding 
intermittently, and with minor oscillations of level. Lastly, coal 
may be formed, as an ordinary sedimentary deposit, by the slow 
accumulation, in quiet water, of deciduous, or other, vegetable 
matter, floated seawards from riparian forests. Hach of these modes 
of formation of coal must have played important parts in the forma- 
tion of coal-seams, at every period of the earth’s history, from the 
dawn of vegetation down to the present day. The exclusive advocacy 
of any one mode is therefore as illogical as it is unnecessary. It 
seems to me that the last mode referred to has not received quite as 
much consideration as its importance deserves, and I propose there- 
fore, while attaching equal importance to the other modes, which 
are already well understood, to consider this particular one in some 
little detail. Before proceeding to do so it may be as well to review 
some of the facts connected with the mode of occurrence of coal- 
seams in general, with a view of arriving at a clearer idea of their 
various histories. 
It is now admitted on all hands that the principal constituents of 
nearly every coal-seam represent so much carbon that has at one 
time existed in the form of carbonic acid in the atmosphere, whence 
it has been extracted by the vital forces of growing vegetation. 
Subsequent pressure accompanied by certain chemical changes, well 
understood, have converted this fixed carbon into coal. The precise 
nature of the vegetable matter forming the coal varies within wide 
limits, not only on account of the varied ages, or the geographical 
position, of the seams themselves; but even within the coal-seams 
belonging to any one geological period and situated at the same part 
of the earth’s surface. There is, further, much diversity in the 
1 I know of no evidence that marine vegetation (i.e. Aly) is capable of conversion 
into coal.—Epir. G.M. 
