126 Kindle — Unconformity at the Base of the 



seen in the photograph just above the bag. The hat rests upon 

 the upper part - of the tilling of the Chattanooga shale. Since 

 the Devonian limestone in the vicinity of Irvine seldom ex- 

 ceeds 10 feet in thickness, it is evident from the photographs 

 that it was locally almost, if not entirely, cut through by sub- 

 aerial erosion previous to Chattanooga sedimentation. Another 

 exposure of the contact of the two formations which occurs in 

 the small ravine between the town and the station at Irvine 

 shows a still more advanced stage of denudation of the lime- 

 stone than that illustrated in the photographs. Here the Devo- 

 nian limestone has been reduced to large disassociated bowlders. 

 These have been enveloped by the Chattanooga shale, which 

 lies upon and around them and rests directly on the subjacent 

 Silurian shale between the bowlders. 



The significance of the remarkable and apparently haphazard 

 variations in the thickness of the Devonian limestone in east 

 central Kentucky to which Foerste* has called attention, 

 becomes evident in the light of the preceding examples of sub- 

 aerial erosion of this formation subsequent to Chattanooga 

 shale deposition. These variations in thickness range from a 

 few inches to 47 feet according to Foerste. Tiie following 

 striking cases are quoted from Professor Foerste's report : f 



" Another thick section of Devonian limestone occurs three 

 miles southwest of Cartersville, where the road to Crab Orchard 

 crosses the headwaters of Harmon creek. Here the Devonian 

 limestone is seventeen feet thick. Half way between this locality 

 and Crab Orchard the thickness of the Devonian limestone is only 

 six v feet, so that the Devonian limestone appears to become thin- 

 ner from both areas toward this middle region. . . . Directly 

 north of Berea the thickness of the Devonian section is thirteen 

 and a half feet. Four miles north of Berea it is reduced to three 

 inches. Evidences of thinning are seen also in going from Berea 

 northeast, toward Bobtown. In the vicinity of' Bob town, and 

 from this region for at least three miles toward the east and north- 

 east, the thickness of the Devonian limestone is reduced to about 

 one foot or less, except at the Mat Moody Store, a mile and a 

 quarter toward the southeast of Bobtown. Here the thickness 

 of the Devonian limestone is at least four. feet four inches, again 

 suggesting an irregular thinning of the Devonian limestone toward 

 the north." 



It would seem to be a reasonable inference that the subaerial 

 erosion which rendered the Devonian limestone cavernous and 

 in places reduced it to a bed of bowlders as at Irvine, may, where 

 the pre-Chattanooga relief was greater, or the drainage more 



* The Silurian, Devonian, and Irvine formations of East-Central Kentucky, 

 Kentucky Geol. Survey. Bull. No. 7, p. 89-92, 1906. 

 t Idem., p. 90. 



