SILURIAN. 233 



The Louisville limestone, which at Louisville is unconformably overlain by 

 Devonian limestone and has a thickness of 55 feet, is described as thinning out 

 toward the north and east. Foerste ^*^'' comments as follows on the relations of 

 Silurian and Devonian: 



The absence of any mention of distinct unconformity at most localities so far examined 

 suggests that the Silurian-Devonian contact is not marked everywhere by strong unconformity, 

 but that at many points in northern Indiana the unconformity is sHght. In the southern part 

 of the State the Silurian-Devonian contact is also accompanied by a shght unconformity. 



The Waldron shale and its abundant fauna constitute the subject of an article 

 by Kindle and Barnett,°°* who refer to the paleontologic work of Hall and state 

 in part : 



The Waldron shale is composed mainly of fine-textured blue to greenish clay shale. Thin 

 bands of impure limestone and calcareous nodules sometimes occur in the shale but represent 

 a comparatively insignificant proportion of the formation. The Waldron shale has a thickness 

 ranging generally from 4 to 10 feet. So far as observed by the writers the Waldron beds are 

 conformable with the Niagara hmestone beds above and below. * * * Although a very 

 thia formation, the Waldron is very persistent and extends southward from southern Shelby 

 and Rush counties to the Ohio River, a distance of about 85 nules. The Waldron shale is not 

 known north of the central part of the State. The heavy mantle of drift to the north of its 

 northernmost exposures in Rush and Shelby counties conceals a large area in which important 

 stratigraphic changes take place, the precise nature of which is unknown. All that we know 

 certainly about them is that they result in a Silurian section in the Wabash Valley in which 

 neither the Waldron shale nor its two accompanying limestone formations have been identi-r 

 fied. It may be that the Cincinnati geanticline, which is beUeved to have been in existence 

 during the Waldron shale interval, as pointed out elsewhere in this paper, swung to the west- 

 ward across north-central Indiana, making distinct marine basins in northern and southern 

 Indiana. Certain differences in the faunas as well as the stratigraphy of the Silurian of the 

 northern and southern Indiana sections could be cited in support of this hypothesis. 



The fauna of the Waldron, which comprises 160 species, is contrasted by Kindle 

 and Barnett with that of the Louisville limestone, with which it has remarkably 

 Uttle in common. Full lists of fossils are given. 



The faunas of the several divisions of the Siliirian in Indiana are distinguished 

 by Foerste,^*^"' who recognizes close affinities between those of the Laurel and 

 Louisville on the one hand and between those of the Waldron and Osgood on the 

 other. 



The divisions enumerated are described particularly from occurrences in 

 southeastern Indiana; in northern Indiana the Niagara strata are not differentiated. 

 The identification of these Niagaran formations and their correlation with the 

 New York section are considered by Foerste. He also identifies a water-lime rock 

 occurring at Kokomo, Ind., as the probable equivalent of the Bertie water lime 

 (lower Cayugan) of the New York State reports. 



The Silurian of Ohio was classified by Prosser ^" hi 1905 as follows : 



Northwestern Ohio. Feet. 



Lucas limestone 



Monroe formation 



Sylvania sandstone 



Tymochtee member (?). 



50-600 



