MINERAL INDUSTRIES OF THE UNITED STATES — COAL PRODUCTS. 5 
tendency of both together is toward providing an increased rate of 
accumulation over that of decomposition. Where conditions have 
been particularly favorable to the maintenance of the relationship 
just mentioned, peat bogs are the result. Peat accumulations as 
much as 40 feet in thickness exist, and while there is a vast gap be- 
tween even a 40-foot peat bog and a 40-foot coal bed when it would 
require the carbon of a 40-foot thickness of peat to yield a 1-foot 
thickness of coal, still, as indicated above, a complete chain of con- 
necting links in material fact exists, and the only leeway for di- 
vergence in theory lies in modifying the details of condition with a 
view to accounting best for the enormous lateral extent and thickness 
of the accumulation. 
Entering into this discussion only sufficiently to derive an ex- 
planation for the present occurrence of coal as a formation between 
the more conventional rock types of shale and sandstone, down in 
the earth’s solid crust instead of on the surface, as its origin would 
suggest, the most satisfactory inference is that of a vast marine 
swamp area gradually sinking. This does not require any stretch 
of the imagination, inasmuch as progressive changes of this order 
characterize the relation between land and sea elevation in general 
to-day. 1 
With the balancing tendencies of a swamp area slowly settling and 
of organic accumulations slowly building, a shallow swampy charac- 
ter of inundation might well be protracted indefinitely, allowing for 
a correspondingly indefinite thickness of peat-like accumulation. 
With the rate of submergence at length gradually gaining the up- 
per hand, vegetation would slowly be drowned out, and the area 
absorbed into sea bottom by the encroaching water. Then in the 
largely land-locked sea area resulting, the relatively calm waters 
would receive the silt from inflowing streams and let it settle quietly 
to the bottom, thus allowing for a continuance of the process of ac- 
cumulation, but causing a change from organic carbonaceous ma- 
terial to that of an inorganic clayey nature. Kealizing the relative 
boundlessness of geologic time, proceedings in this stage in the evo- 
lutionary process would be capable of any degree of extension, re- 
sulting in the burial of the organic deposit under an indefinite 
thickness of sediment whose character might change with changing 
conditions of submergence from essentially clayey to essentially 
sandy, or essentially calcareous matters, yielding almost any thick- 
*For instance, to the northward of the general vicinity of New York the land 
of the coast line is subsiding while to the southward the reverse is true. Inci- 
dentally it is the advancing water boundary with its encroachment upon the 
land surface in the one case, and the receding water boundary with its conse- 
quent exposure of beach area in the other, which accounts for the rugged New 
England coast and a flat sandy South Atlantic coast. 
