340 AMADEUS W. GRABAU 



or scales of dry, gray mud, which were then incorporated in the 

 black mud. This is just what we should expect if the deposition of 

 the gray muds had come to an end and sedimentation were renewed 

 by the influx of the black mud from another source. Essentially, 

 however, deposition here was continuous, and after the commence- 

 ment of the sedimentation of the black Huron mud, there was a 

 temporary recurrence of the gray sedimentation, so that we see 

 today a io-foot bed with all the characters of the typical Olentangy 

 lying above a considerable thickness of black Huron shale. In 

 both the upper and the lower part of this interbedded mass of 

 Olentangy occur thin bands of black shale, as they do in the typical 

 Olentangy lower down. 



The basal contact of the Olentangy and Delaware is not shown 

 in any section which I visited, but the Olentangy could be examined 

 to within a few feet of the contact. There is no interbedding of 

 the Delaware and the Olentangy; the change in material is abso- 

 lute. The concretionary limestones of the Olentangy are very 

 different in character from the calcarenytes of the Delaware 

 limestone. The concretions appear to be of the subsequent type 

 found in the gray Cashaqua shales of western New York, to which 

 the Olentangy shales bear the closest resemblance. Like them, 

 they are unfossiliferous, though fossils are found in some parts of 

 the Cashaqua. The barren nature of both of these shales is in 

 striking contrast with the highly fossiliferous character of the 

 Hamilton shales of western New York, Canada, Michigan and even 

 northern Ohio. A few fragmentary fossils have been found in the 

 calcareous beds, but these might easily be residual specimens 

 weathered from the underlying limestones and incorporated in the 

 new sediment. Such undoubtedly is the origin of the lenticular 

 bed of crinoid fragments found in the type section, which does not 

 exceed 5 inches in thickness. This is apparently a reworked mass 

 of crinoidal fragments dissociated by the weathering of an older 

 crinoidal limestone. 



The relationships here presented admit of only one conclusion, 

 namely, that the Olentangy shale is a part of the Upper Devonian, 

 representing a special type of sedimentation, such as characterized 

 the early Upper Devonian sediments of western New York. Sedi- 



