62 GEOLOGICAL REPORT. [1101 



III. Rotten Ltmestone Group. — Soft, chalky, white limestones 

 of great uniformity and thickness, passing into heavy calcareous, 

 massy clays, or light colored clay marls. Fossils numerically 

 abundant, but species few. Characteristic are : Placuna scabra; 

 Janira quinquecostala; Gryphaa convexa, mutdbilis, Pitcheri: Ostrea 



falcata; Rudistae ; Mosasaurus. — Underlies the prairies. 



IV. Ripley Group, Con. — Hard, crystalline, white limestones 

 (generally somewhat sandy and often glauconitic), underlaid by 

 black or blue micaceous marls, whose fossils are in an admirable 

 state of preservation. Prominent among the latter are Cardium 

 Tippanum and Spillmani, Cucullcea capax and Tippana, Gervillia 

 ensiformis, Siliquaria biplicata, Dosinia densata, Crassaiella Rip- 

 leyana, Baculites Spillmani and Tippaensis, Scaphites Iris — also 

 Scajphites Conradi. Ammonites placenta, a large Atktha? with sharp 

 revolving costae, and others. The fossils of the hard limestone 

 differ in some respects from those of the marl. These strata form 

 the Pontotoc Ridge in Mississippi, and Chunnenugga Ridge in S. 

 E. Alabama ; according to late researches by Conrad, they also 

 exist at Eufaula, Ala. 



I. THE EUTAW GROUP. 



("lower CRETACEOUS" or TUOMKV.) 



101. The territory indicated on the map (by the olive green tint) 

 as being occupied by this formation, offers no strikingly charactistic 

 features. By far the larger portion of its surface is thickly covered 

 with the strata of the Orange Sand, from which the upper, sandy 

 members of this group are often distinguished with great difficulty 

 — it being some times, in fact, optional with the observer, as to 

 which view of their age he may choose to take (138-39). It is 

 even so, at times, with the laminated clays found in the region, 

 which characterize the lower portion of the cretaceous deposits as 

 well as those of the Orange Sand. Usually, the fat, compact, 

 bluish lamina) of the cretaceous clay (popularly called "Soap- 

 stone"), are sufficiently distinct in their aspect and touch from the 

 more sandy, and commonly micaceous, clay deposits of the Orange 

 Sand ; and in almost all cases there is one available mark of 

 distinction : the ferruginous selvedges and stratification lines of the 

 cretaceous clay, are yellow (hydrated peroxide) while those of the 

 Orange sand are almost uniformly red (anhydrous peroxide.) These 



