1131] LOCALITIES OP RIPLEY GROUP. 85 



into a ridge, are formed by the marl strata underlying the rock, capped usually 

 by the Orange Sand. Such is the case in Tippah, in middle Pontotoc, and in 

 Chickasaw county, N. E. of Houston. The Pontotoc Ridge is therefore, in fact, 

 rather a belt of ridgy land, which is in several instances (Chiwapa, Ohuckatonche) 

 traversed by streams, though more commonly, it forms a "divide," between the 

 waters of the Tombigbee and Hatchie on one side, and those qf the Tallahatchie. 

 Loosha-Scoona and Yallabusha on the other. 



Interstratified with the blue marls, and in some instances repla. 

 cing them entirely, we find strata consisting of sandy limestone of 

 various degrees of induration within its own mass, so that the 

 action of water wears it into fanciful, often perforated forms, 

 which have obtained for it from the inhabitants the names ol "bored 

 limestone" and "horse-bone limestone.'" It abounds in fossils, 

 which are, however, generally preserved as nuclei only. 



131. Localities of the Ripley Group. — The most northerly outcrop which 

 I know to exist, occurs near Joncsboro, on S. 11, T. 2, E. 4 E., Tippah county. 

 Here we find outcropping on the sides of a small valley, a ledge 12 to 15 inches 

 thick, of hard crystalline limestone, somewhat sandy, with grains of greensand 

 interspersed. Its weathered surface is covered with projecting fragments of 

 shells, chiefly of a large Turritella (allied to T. Bauga D'Orb., and different from 

 T. Tippma Con. of Owl Creek), of Gryphaea vomer, a large Venericardia with 

 flat radial costte, and claws of a Gallianassa. This rock is so hard that it has 

 been used for millstones ; a fine chalybeate spring issues from beneath the ledge. 

 A soft ferruginous variety of it, into which it shows occasional transitions, is 

 said to crop out on Muddy Creek, due W. of the locality mentioned, while half 

 a mile E. of it, the soft shell marl was found in wells. 



At Mr. Wilhites, S. 27, T. 2, E. i E., a well was dug on a hill, at the foot of 

 which the blue Owl Creek marl, with numerous fossils, crops out. The section 

 thus obtained is as follows : 



