THICKNESS OF SILURIAN SUBDIVISIONS 415 



formably overlaid by the Laurel limestone, is increasing instead of de- 

 creasing in thickness eastward. Moreover, the Laurel limestone, which 

 has been gradually increasing in thickness from Newsom northeastward, 

 as far as Bledsoe, is only 18.5 feet thick at the S. R. Wood locality, and 

 disappears a short distance east of Weeks' house. 



At Baker 17 J feet of Louisville limestone disappear in a distance of 

 half a mile southeastward. 



There is no diminution in thickness of the Laurel limestone between 

 Newsom (locality 12) and the Johnson V. Linton locality (locality 15) ; 

 on the contrary, there is a slight increase. Nevertheless, in a distance 

 of 2 miles southward the entire Laurel section, the equivalent of the 

 Osgood bed, and the upper parts of the Clinton limestone have disap- 

 peared. This is estimated to be a decrease in thickness of 25 feet per 

 mile. Between the J. Linton, Jr. (locality 16), and the J. Linton, Sr. 

 (locality 17), localities, the Clinton diminishes from 16.5 to 2 feet in 

 three-quarters of a mile. The rate of diminution between Newsom and 

 the J. Linton, Sr., locality is 14 feet per mile. Between the locality 

 2 miles west of Tank (locality 14) and the W. M. Forehand (locality 

 13) locality, however, it is calculated to be at least 40 feet per mile, 

 involving all the formations below the Waldron shale horizon. In 

 striking contrast with this is the comparative constancy in thickness of 

 the Laurel and Osgood sections at numerous exposures between Newsom 

 and Pegram, also in an east and west direction although farther north- 

 ward. 



Near Fly (locality 19) the Silurian section diminishes about 70 feet 

 in one mile going southward; east of C. E. Harris' it diminishes about 

 30 feet, and east of Mat Sowal's, about 40 feet per mile. 



Between Montgomerys mill (locality 27) and Centerville (locality 25), 

 in a distance of about 6 miles, the Laurel limestone seems to diminish 

 in thickness from 28 feet to 25 feet. This is of very little significance, 

 when the difficulty of discriminating between the top of the Osgood bed 

 and the base of the Laurel limestone in these southern sections is con- 

 sidered. In striking contrast with this regularity in thickness is the 

 almost entire disappearance of the Laurel limestone within a distance 

 of 8 miles, if the 2 feet of limestone immediately beneath the Black 

 shale at Tan Yard hollow (locality 22) be accredited to the Laurel 

 horizon. If this identification is not correct the Laurel has entirely dis- 

 appeared. In a distance of 6.5^ miles between Centerville and Fogg 

 (locality 20), all except the lower 5 feet of the Clinton have disappeared. 

 This is a diminution of about 10 feet per mile. This rate of decrease is, 

 however, much exceeded toward Sam Turner's house (locality 24), where 

 the rate is about 40 feet per mile. Between Tan Yard hollow (locality 



