AGE CHARACTERISTICS OF COALS 
143 
in well-defined valleys. The lens-like form has been emphasized 
by all observers in every portion of the Tertic belts. Unfortunate¬ 
ly the details recorded for most regions are insufficient to justify 
any attempt at working out the history of any bed known to cover 
a large space. Detailed study is, in fact, impossible at present 
either in the United States or Canada, where alone the great beds 
are known, because they occur in districts with sparse population, 
and where for long distances, one must depend upon imperfect 
natural outcrops, or on the less definite lines of clinkered rock 
caused by the spontaneous combustion of the coal. The per¬ 
plexity is increased by variations in thickness and composition of 
the intervening rocks, as well as by similar variations in the coal 
beds themselves, all of which make correlations extremely diffi¬ 
cult. 
Some American observers, notably Keyes, Bain and Winslow, 
decline to regard coal deposits as continuous over large areas, 
but prefer to describe “coal horizons.” All agree to the lens-like 
character of many beds; even those who are unwilling to accept 
this for the great beds frankly present the frequent changes into 
shale and the local disappearance of the coal as serious problems. 
Some observers have shown that the lenses often overlap, that 
the coal thins out, and may be replaced by another a few feet 
higher or lower. This feature, so characteristic of American 
localities, was early recognized by Credner and by Raefler in the 
coals of Prussian Saxony. 
The intimate resemblance of many brown coal deposits to those 
of peat has been affirmed by many observers. Collier recognized 
the resemblance in Alaska and Washington, as also did Eldridge 
in Alaska; Haast was positive respecting it in southern New 
Zealand; several authors have described it the Moorand Moos- 
kohle of Prussia and Bohemia; Gothan and Horich have shown 
that the Torfdolomite of the Lower Rhine is merely mature peat 
replaced by inorganic matter; Smith and Travers described as 
peat an impure brown coal underlying the London clay. 
The carbon content of brown coal varies. In a general way 
it gives proof of great advance over peat. Yet in many localities 
the process of conversion stopped short of the stage reached by 
most of the fuel peats of which analyses are available. Pliocene 
coal of Bavaria has from 62 to 69 per cent; Miocene coal from one 
mine in Bavaria has but 49; the Edeleny coal of Hungary has 
