294 C. SCHUCHERT MEDIKA AND CATARACT FORMATIONS 



contacts in this area are always easily made out^ — a sandstone on a shale. 

 As the Medina thins out to the northwest, so the Cataract thickens in the 

 opposite direction, heing- 54 feet in the Xiagara Gorge, 80 feet at Grimsby, 

 90 feet at Stony Creek, Hamilton, and Dunda.s, and 105 feet or more to 

 the northwest. 



At first the writer intei-preted these shar]3 contacts as disconformities ; 

 but he now sees, on the basis of the faunal evidence, that tliis interpreta- 

 tion is not the correct one. Further, the Stony Creek section shows 

 practically a complete and sandy transition from the Cataract into the 

 Medina. In other words, the top of the Medina — that is, the typical 

 Medina, about 60 feet thick — gradually loses its sandy character from 

 Thorold northwestward and is transformed first into sandy shales and 

 then into argillaceous shales, the Cabots Head or topmost rnember of the 

 Cataract. On the other hand, the two lower members of the Cataract — 

 the Whirlpool sandstone and the Manitoulin limestone — maintain their 

 Ontario petrologic characters into the Niagara Gorge (see plate 13 and 

 'plate 14, figure 2). Finally, the latter member is either absent or modi- 

 fied at Lockport, while farther east both are absent. As the Medina and 

 Cataract have at least 7 species in common, the easily discerned contax^ts 

 between these formations as seen from Xiagara Gorge to Dundas can not 

 be interpreted as disconfonnities. In other words, the typical Medina 

 formation shades through lateral alteration into the typical Cataract. 



Even though the Medina, Cataract, and Brassfield are correlates of one 

 another, it does not follow that each one is wholly the equivalent of any 

 other. Each formation invades eastern Xorth America from a different 

 direction and each one has its own peculiar faunal assemblage (see 

 figure 1 ) . They therefore represent three physical provinces and marine 

 basins. The Medina is of the northern Appalachian province, is a sand- 

 stone formation, and finally invades to a slight extent the area of the 

 Cataract. The Brassfield province lies in the main west of the Cincin- 

 nati axis, is of southern origin, with limestone-making seas, spreads also 

 up the southern portion of the Appalachian province, and finally invades 

 slightly the area of the Cataract sea. On the other hand, the Cataract 

 province spreads westward through the Saint Lawrence embayment, and 

 finally in eastern Ontario and northeastern Ohio (known from the Clin- 

 ton oil wells) unites with the other two provinces; but as the Medina' 

 waters form a shoal sandy area in northeastern Ohio between the other 

 two provinces, very few of the species of either area intermigrate. Prob- 

 ably it would be more correct to state that the normal marine junction of 

 the Cataract and Brassfield seas is prevented by the Medina delta. For 

 these reasons Medina, Cataract, and Brassfield are to be retained as 

 names for independent marine faunas and formations. 



