764 T. E. SAVAGE 



According to this view, the dull laminae and mineral charcoal 

 partings of the coal beds are the records of repeated interruptions 

 of accumulation, during which the surface of the vegetable material 

 in the swamp was above water and exposed to atmospheric decay, 

 resulting in the destruction of the softer parts of the plant tissues, 

 leaving them in an indurated and more or less skeletonized and 

 fibrous condition. On resubmergence these residual portions of 

 the vegetable materials were not so readily impregnated with the 

 fundamental matter of the bog as were those parts of the mass that 

 had not suffered partial atmospheric decay, and hence are of dull 

 appearance. Such periods of arrested accumulation of the plant 

 material, due to the exposure of the surface of the vegetable matter 

 of the bog, would be favorable for the accumulation on such a 

 surface of a relatively larger proportion of spores than would be 

 mingled with the vegetable mass during periods of submergence 

 and of normal vegetable growth in the bog, and the resistant nature 

 of the spore cases would permit their better preservation than the 

 ordinary plant tissues during such times of exposure. These con- 

 ditions would explain the greater abundance of spores in the dull 

 than in the bright laminae of the coal beds. The variation in 

 thickness of the dull laminae would be due to the unevenness of 

 the surface of the exposed vegetable matter in the bog. The rela- 

 tively smaller percentage of volatile matter and larger percentage 

 of fixed carbon in the dull laminae and mineral charcoal would be 

 explained in part by the fact that, during the times when the surface 

 of the vegetable mass was above water and exposed to atmospheric 

 decay, the volatile products of decomposition escaped into the air, 

 and in part because the dull laminae were not subsequently infil- 

 trated with the hydrocarbons of the fundamental matter to the 

 same extent as the bright laminae. 



The foregoing interpretation of the structural features of the 

 coal beds leads to the following very definite conclusions : 



1. That the beginning of vegetable accumulation of the coal 

 beds was in a very shallow swamp. 



2. That the swamp deepened so slowly, either by subsidence 

 of the area or from the gradual building-up of the border or outlet 

 by sedimentation, or both, that the plants were able to adjust them- 



