PROGRESSIVE OVERLAP 609 



Phacops rana. This is a Hamilton or later fauna, and although the 

 fauna of the Black shale includes Leiorhynchus limitare and Agoniatites 

 vanuxemi, both of them typical Marcellus species, the fauna as a whole 

 is certainly Upper Devonic (Naples-Portage), as stated by Williams. 

 The same thing may be said of the Hot Springs section; for here the 

 Buchiola speciosa fauna is abundant only 70 feet above the Black shale, 

 60 feet of the interval immediately below the shales with this fauna being 

 concealed. In the 9 feet of white or cream colored shale immediately 

 over the Black shale occur Orbiculoidea doria, Bellerophon leda, and 

 Styliolina fissurella, besides others unidentified specifically. The Black 

 shale itself contains Orbiculoidea doria, Styliolina fissurella, and ques- 

 tionably identified Chonetes cf. coronatus, and Anoplotheca cf. acutipli- 

 cata. The evidence adduced, then, points to an early Upper Devonic age 

 of the Black shales at Hot Springs, rather than a lower Middle Devonic, 

 as advocated by Williams. The Black shale is 10 feet thick and rests 

 upon Oriskany (?) sandstone. 



In Allegany county, Maryland, the Black shale forms the base of the 

 Bomney formation, which has a thickness of about 1,600 feet. Here the 

 shale is clearly of the age of the Marcellus of New York, and in part 

 it also represents the Onondaga. This portion of the formation rests 

 upon the Oriskany and has a thickness of about 500 feet. The upper 

 1,100 feet of the Bomney contains a typical Hamilton fauna.* Eastward 

 from this, in Washington county, the Hamilton division of the Eomney 

 overlaps the Marcellus, which is only sparingly represented, f 



We have here clear evidence of a continued southwestward progression 

 of the encroaching sea, and a corresponding progressive overlap of the 

 higher formations southward. In all cases a basal black shale occurs, 

 rising in the scale from Marcellus or lower in the north to uppermost 

 Devonic and, as indicated in Big Moccasin Gap, to Lower Carbonic. 



At Irvine, Kentucky, the Black shale again lies high up in the series, 

 for here it has intercalated in its upper part calcareous and ferruginous 

 concretionary sheets which carry undoubted Lower Carbonic fossils. 

 These occur in the sections before the Black shale loses its characteristic 

 expression. J 



In the London quadrangle of central Kentucky the Chattanooga shale 

 rests on Devonic limestones with an erosion interval. It has a thickness 

 of 150 feet, is very black and bituminous. It is succeeded upward by 

 a light blue clay shale and argillaceous sandstone, the shale abounding 

 in light blue or drab ironstone concretions. Many siliceous concretions 



* Prosser : Journal of Geology, vol. xii, p. 361. 



t Ibid. : Loc. cit., p. 362. 



% Williams : Amer. Jour. ScL, vol. Ill, 1897, p. 398. 



