132 E. C. Case — Ampliibian Fauna at Linton^ Ohio. 



material, due to minor changes induced by slight but repeated 

 and rapid fluctuations of level, they maintain on the whole a 

 homogeneity which speaks of widespread and long continued 

 uniformity in the general aspect of the land and water. Per- 

 haps the best picture that has been presented of the region is 

 that given us by David White in Bulletin 38 of the Bureau of 

 Mines, page 63 : 



" Summary of Terkestrial Conditions. 



Coal formed on subsiding areas. 



On the whole the criteria relating to the terrestrial condi- 

 tions of deposition show that the formation of widel}^ extended 

 coals in series were regions of subsiding base-level coastal 

 plains or filled basins. That the rate of subsidence was vari- 

 able is shown by the varying character of the rocks of the coal 

 measures ; the presence of marine faunas in places immediately 

 above the coal ; the occurrence of shallow water limestones, of 

 ripple-marked, rain-marked, or sun-cracked layers or of con- 

 glomerates or local unconformities : and in particular the 

 occurrence of great thicknesses of coal covering large areas. 

 The deposition of the great thicknesses of peat necessary for 

 the production of a thick bed of coal, probably 10 to 20 feet of 

 peat being required to produce a single foot of high-grade 

 bituminous or semi-bituminous coal, could hardly have taken 

 place except under such close adjustment of the rate of sub- 

 sidence to rate of peat accumulation as to maintain a depth of 

 water cover within limits that would permit the growth of 

 peat-forming vegetation for an exceedingly long time. Too 

 rapid a subsidence would have flooded the swamps so deeply as 

 to kill the principal peat-forming vegetation, produce open 

 water conditions, and allow the invasion of sediment-bearing 

 water with its oversweep of mineral matter, or of oxygenated 

 water which would have permitted the advance of decay 

 (biochemical process), to the complete destruction of the super- 

 ficial organic matter, unless the deposition of sand or mud were 

 sufiiciently rapid quickly to arrest the decay by exclusion of 

 the sources of oxygen supply. The roofs of many coal beds 

 bear evidence of the latter conditions. In most cases, how- 

 ever, the oversweep of clays and sands appears to have been so 

 abrupt as to seal the underlying more or less aseptic organic 

 mass from access of oxygen and to prevent its continued 

 decomposition. On the other hand, if the subsidence of the 

 region was too slow or there was warping of the region, the 

 surface of the peat may have reached the upper limit of its 

 formation and entered the zone of increasing exposure (insuf- 

 ficient water), in which the organic matter was reduced to 



