764 T. C. CHAMBERLIN 



southward until the rising of the Carboniferous beds in the bot- 

 tom made further extension in that direction unpromising. Only 

 a few feet beyond the end of the original tunnel Carboniferous 

 shale was found overlying the heavy stratum of limestone, and 

 the surface of this rose as though the foot slope of the ridge 

 had been reached. The correctness of this inference is scarcely 

 open to question as the whole environment supports it so 

 strongly that it had been anticipated. The ease with which this 

 shale was eroded, compared with the underlying limestone, 

 readily explains the flat limestone surface on which the tunnel 

 was run. 



In an excavation on the west side of the tunnel, a shallow 

 trench was found in the upper surface of the limestone running 

 nearly parallel with the tunnel and also parallel to the axis of 

 the adjacent ravine. With little doubt this trench was the axis 

 of the ravine in the erosion stage just preceding the filling up 

 of the ravine by the relic-bearing deposit. This further aids in 

 explaining the nearly horizontal, but slightly rising, base of the 

 tunnel, since it locates it alongside the axis of the ravine on a 

 resistant bed (see Fig. 13.) 



An offset tunnel at right angles to the original tunnel was 

 run eastward eleven feet from the place of the adult skeleton. 

 It developed about four feet of disturbed shale and mixed debris 

 in its base, the vague structure lines of which dipped eastward 

 irregularly. It had the appearance of a talus slump that had 

 crept down the slope of the adjacent rock surface, and warped 

 and slightly tilted itself backwards according to a common habit 

 of such masses. This doubtless took place before the upper 

 deposit was laid upon it and while yet the ravine was open, i. e., 

 about the close of the erosion stage. In the east end of this 

 offset, the silty formation has been slightly fissured along a nom- 

 ber of lines by tensional action and the little crevices filled with 

 a grayish-white soft deposit that effervesced very promptly with 

 acid, implying calcium carbonate. The riveing tension probably 

 came from the tendency of the mass to creep on the underlying 

 rock surface, since this rises to the east and so furnishes a slop- 

 ing base of shale which arrests the waters descending through 



