AGE CHARACTERISTICS OF COALS 
149 
Tertic, coals not all the accumulations of vegetable materials had 
attained the same degree of enrichment before burial. The 
minimum for the Pierre analyses seldom falls below 75; yet there 
are some seams with only 71 or 72. The peculiar condition is 
well marked in the Hanover district where the “black coal” has 
89 per cent, of carbon, the brown coal 73, and the Blatterkohle 
is almost unchanged, yet the several types occur in the same 
vertical section. 
Jurassic and Triassic areas containing coals in economic quanti¬ 
ties are utterly insignificant when compared with those in which 
the rocks of these ages are exposed; but there are many localities 
in which coal materials accumulated during brief periods and 
amid unfavorable conditions. Oolite coals of Britain and the few 
spots on the continent of Europe are of inferior quality, and are 
merely local and without especial interest. Elsewhere the useful 
deposits are in the lower part of the Lias formation. The Jurassic 
succession above the Lias horizon and the Triassic below the 
the Keuper formation may be regarded as barren. 
The strata associated with the coals are similar to those dis- 
♦ 
played in the later periods. The Oolite coals of England are 
intercalated in sands. The Jurassic coal beds of Spitzbergen 
are confined to the Middle, or Sandstone, division as defined by 
Nathorst. The Grestener, or coal-bearing Lias of Austria is com¬ 
posed of sandstones and shales. Similar conditions prevail in the 
Liassic coal areas of Hungary and Siberia. The Jura-Trias 
section of Queensland and New South Wales is almost wholly 
sandstone. 
The Late Triassic section in Austria and Hungary is sandstone 
mainly, with some intercalated shales. On the other hand the 
Jurassic coal bearing rocks of Alaska are almost entirely shales; 
the Late Triassic deposits in some small areas have little sand¬ 
stone. 
Freshwater fossils in rocks associated with coal seams have 
been observed in England, Siberia, Spitzbergen, France, and 
Queensland. The structure of the rocks is evidence of, at most, 
shallow water; and in some cases it is very suggestive of eolian 
agency. False-bedding is _ reported from England, Australia, 
Germany, and North Carolina; and ripple-marks are common 
features at many places. Sandstones and shales frequently con¬ 
tain logs of wood, in such relations as to leave little room for 
doubt that they were simply stranded materials. 
