3^74 Annals of the Carnegie Museum. 



6. V^ery clayey limestone with marine fossils. 



Pine Creek horizon. 2 ft 2 ft. 



5. Green clay. 10 ft ^2 ft. 



4. Sandy shale. 3 ft '5 ft. 



3. Heavy-bedded sandstone. Buffalo horizon. 41 ft. 6 in 56 ft. 6 in. 



2. Black limy shale with numerous marine fossils. Brush Creek 



horizon. I ft 57 ft. 6 in. 



I. Thin-bedded rather sandy shale. Mason horizon. 17 ft 74 ft- 6 in. 



On the opposite side of the small ravine the section is very different. 



9. Thin-bedded green shale. 21ft 21ft. 



8. Red, iron stained clay with marine fossils. Horizon unknown. 



lit. 6 in 22 ft. 6 in. 



7. Red clay. 11 ft. 6 in 34 ft- 



6. Sandy shale with lenses of sandstone toward the top. 62 ft. 6 in. 96 ft. 6 in. 



5. Heavy-bedded sandstone with occasional lenses of sandy shale. 



48 ft. 6 in '45 ft- 



4. Sandy shale. 8 ft '53 ft- 



3. Clayey limestone with marine fossils. Brush Creek horizon. I ft. 154 ft- 

 2 Thin-bedded sandy shale with plant remains. Mason horizon. 



17ft '71 ft- 



I. Green clay. 5 ft ''76 ft. 



Just before the ravine is reached, the Pine Creek limestone, the 

 clay beneath it, and the upper part of the Buffalo sandstone are cut off 

 as indicated in the diagram and shown by the photographs (Plate 

 XIII). A little beyond the ravine the base of the combined sand- 

 stones cuts down through the Brush Creek limestone, the Mason 

 shale, and the clay beneath it. About half-way between this ravine 

 and Jack's Run the Pine Creek limestone and its clay reappear in the 

 face of the cliff and the base of the Buffalo sandstone again comes 

 above the level of the track. On the northern side of Jack's Run the 

 Pine Creek limestone is 100 feet above the level of the track. 



From the diagram and the sections on which it is based, it is very 

 evident that there must have been two periods of erosion, one before 

 and one after the Pine Creek limestone was deposited. From the 

 depth and narrowness, and the steep sides of the valleys cut during 

 both these intervals it is evident that the land must have been raised 

 some distance above sea-level after each marine formation had been 

 deposited, and from the sharp truncation of the edges of the strata 

 (see Plate XIII), it would seem that the rocks were rather firmly con- 

 solidated before the erosion took place. 



The area eroded after the Brush Creek limestone was deposited was 

 quite extensive, as is indicated by the distribution of the Buffalo sand- 



