78 GEOLOGICAL REPORT. T119, 120 



which and the Rotten Limestone there appears to he a zone of transition, char- 

 acterized, among others, by the frequent occurrence of hard ledges of conglo- 

 merated shells, and of Baculites gigas; while having some shells in common 

 with both groups. Outcrops of this character on the upper Hatchie and on 

 Old Town Creek, will be described under the head of the Ripley group 

 (1T134.) 



Near (\V. and N. W. of) Danville, Tishomingo county, bald prairies are said 

 to occur. The occurrence of the white "joint clay" at Polk's cut has been 

 menticned (TfllO, Bee. 7.) 



119. At Boone's cut, S. 16, T. 5, R. 7 E., on the Mobile & Ohio R. R. (about 

 3 miles N. W. of Boyer's mill — ^flll) a section of about GO feet is obtained in 

 the cuts and branches. In the cuts, the white, calcareous "joint clay," teeming 

 with Grypham mutabilis, is underlaid by "blue rock," but there is no stratifica- 

 tion line between ; the "joint clay" conforms to the surface of the hills, and 

 every stage of transition from the one to the other may be traced, showing that 

 the difference in aspect is owing to atrncspheric influences. Still further down- 

 ward, the "blue rock" passes over into a blue, micaceous, non-effervescent sand 

 similar to that on Okalilly (Hi 12). Such, probably, on a larger scale, is the 

 succession of strata in the deep wells mentioned in R. 6 E. — A few mUes W. of 

 Boone's cut, bald prairie hilltops; appear, with abundance of shells. 



At Mr. William Yates', S. 11, T. 6, R. 6 E., bald prairie spots are common, 

 and clusters of Gryphaeae cemented by calcareous sand (similar to that of the 

 upper stratum on Okalilly — H112) were taken out of his well. 



Both tlie localities just mentioned are on the eastern edge of the Rotten 

 Limestone region. Due W. of it, near Blackland, the characteristic rock appears 

 abundantly in the beds of the creeks, and thence constantly on the road to Car- 

 rollville; good exposures occur on Twenty mile Creek. 



120. Due E. of Blackland there rises a high ridge, on the summit and in the 

 ravines of which, the marl of the Ripley group appears, with its characteristic 

 fossils. 



In T. 6, R. 5 E., Tippah county, the dividing ridge between the waters of 

 the Hatchie and Tallahatchie, and those of the Tombigbee, also forms the line 

 between the Rotten Limestone and the Ripley Group; the former, or its equiv- 

 alents, crop out with frequency on the creeks of the S. B. slope, especially on 

 the main Tishomingo, and on Yoonaby Creek. On the hills in which these 

 creeks head, there are numerous "bald prairie spots," on which Eyogyra and 

 Grypfiaeae are lying about. 



A bluff on Tishomingo Creek, near Mr. J. II. Kennedy's, S. 14, T. 6, R. 5 

 E., affords a remarkably fine opportunity for study ; similar exposures are 

 found on the creek for several miles — 'i he bluff is about GO feet high ; a blu- 

 ish, soft, somewhat sandy marl, the uppermost 8 feet of which consist of a ma- 

 terial rather more clayey than the rest, of a yellowish tint, and very similar to 

 the Rotten Limestone of the hilltops. Among its fossils, which are numerous 

 and well preserved, are Exo, yra costata, GrypJiaea mutabilis and convexa, (incur- 

 vaT), Ostrea falcata, crrtaceaf, Anemia argentcaf, Placurux tcabra, 



