STRATIGRAPHY OF OHIO WAVERLY FORMATIONS 777 



Ft. In. 



3. Coarse quartz sandstone, grains well sized and rounded, white in 

 color, harder and with much less iron than the other beds. This 

 is Conglomerate II of Herrick and the bed which forms the top 

 of the Black Hand in Prosser's description of this section \-6 



2. Allerisma winchelli horizon, a hard, bluish, gritty shale with a 

 considerable fauna, chiefly of lamellibranchs and abundant Spiro- 

 phyton markings, one of the most important horizons in central 

 Ohio 5 



I. Very coarse, loosely coherent, reddish sandstone, grains uni- 

 formly sized and all about one millimeter in diameter, rounded 

 or subangular. Lower surface slightly irregular i 4 



Evidence of erosion of the underlying beds before some of the 

 coarse members were laid down is not unusual. Both at Rush- 

 ville in Fairfield County and at Newark the topmost bed of the 

 Byer sandstone had been eroded slightly before the basal bed of 

 the Allensville was laid down. The fossils in the Allerisma shales 

 are practically always found in the attitude which they maintained 

 during life, the shells of Prothyris standing vertically with the 

 anterior end downward, the shells of Allerisma, Grammysia, and 

 Sphenotus standing obliquely with the anterior end downward. 

 At Newark these shells have been observed at the top of the Aller- 

 isma shale with the upper portion beveled off at the contact with 

 the overlying coarse bed (Conglomerate II). Evidence of erosion 

 is also seen at the base of some of the higher coarse lenses when they 

 are well developed. Obviously the erosion observed in connection 

 with most of these beds is local. This urges caution in accepting 

 the erosion which took place prior to the formation of the lowest 

 bed as any more important. It is, however, probably of somewhat 

 greater significance since in central Ohio it inaugurated an abrupt 

 change in conditions of sedimentation. In the southern counties 

 no evidence of such erosion has been seen, and the change in the 

 conditions of sedimentation was more gradual. Among numer- 

 ous interesting problems is the occurrence of these slight erosion 

 surfaces associated with the finer beds of the member, whereas to the 

 southward where the beds are coarser the evidence of erosion, if 

 present at all, is less prominent. 



Curious and probably of considerable significance is the manner 

 in which the Allensville bed disappears from the column in southern 



