Ripley Island Area of Southern Indiana. 333 



Hebertella near occidentalism and Hebertella near sinuata, 

 Platystrophia Madison bed form, Platystrophia acutilirita, 

 Rafinesquina alternately Ctenodonta cingulata, Schizolopha 

 moorei, and Protarea vetusta. Ten feet below the base of the 

 Silurian section occurs limestone corresponding to the compara- 

 tively nnfossiliferous limestone at the base of the quarry a mile 

 northeast of Osgood, and to the top of the exposures at the north 

 end of Versailles. 



About 5 miles northwest of Zenas, and 6 miles west of the 

 Hone} 7 creek locality, near the mouth of Painter creek, a mile 

 and a half southeast of Westport, the top of the Ordovician, 

 exposed in a vertical section 15 feet thick, contains the follow- 

 ing fossils, which have been listed also from other localities 

 farther east : Dalmanella small species with very convex 

 brachial valves, Hebertella near occidentalism Hebertella sinu- 

 ata, Madison bed form of Platystrophia, Platystrophia acuti- 

 lirita, Leptaena rhomboidalis, Strophomena sulcata, Stropho- 

 mena vetusta, large form of Plectambonites strongly deilexed 

 anteriorly, Rhynchotrema capax, Trematis millepunctata, 

 Protarea vetusta, Streptelasma rustic um, and Streptelasma 

 divaricans. Dinorthis subquadrata, not noted so far at this 

 horizon, occurs also. 



From Yersailles the top of the Madison bed is exposed 

 almost continuously along Big Graham creek as far as Benville. 

 At New Marion the fossiliferous clayey beds overlying more 

 solid limestones produce a section easily recognized as equiva- 

 lent lithologically and faunally to that at the top of the Madi- 

 son bed at Versailles. Four miles north of Benville, a mile 

 and a half south of Nebraska, the banks of Otter creek expose 

 a considerable section of Richmond rocks, about 60 feet thick, 

 all of which is placed in the Madison bed, being regarded as a 

 nearly complete section of the Madison bed at this locality. 

 The fossils include the Madison bed form of Platystrophia, 

 Hebertella n ear sinuata, and Streptelasma divaricans. At some 

 horizons bryozoans are rather common, and their study may 

 accomplish much in the future in confirming or combating 

 the views here expressed, since the bryozoans are better horizon 

 markers as a rule in the Cincinnati formations than the brachi- 

 opoda. In fact, the observations here recorded are direct 

 evidence of the limited value of brachiopoda as horizon markers 

 since most of the species here listed for the first time from the 

 Madison bed have long been known from lower horizons in 

 the Richmond. 



Unconformity betvieen Madison and Niagaran beds com- 

 paratively small. — The thickness of the Madison bed varies in 

 an irregular manner in Indiana and western Kentucky, but in 

 general there is a decrease in thickness on passing from Madi- 

 son southward toward central Kentucky. In the opposite 



