342 AMADEUS W. GRABAU 



faunas is fully set forth in the unpublished report referred to. 

 There, too, it is shown that the faunas of the Traverse group on 

 opposite sides of the state of Michigan differ materially, while 

 identification of equivalent limestones and shales between the two 

 sections is impossible. All of these facts would lend some force to 

 the suggestion that precise correlation of the Prout limestone and 

 Plum Creek shales with the Encrinal limestone and Arkona shales 

 of the Thedford region should not be too rigidly insisted upon. 

 Nevertheless, we may with Stauffer lay much stress on the presence 

 of the Bactrites layer at about 25 feet below the Encrinal at Arkona 

 and a similar distance below the Prout limestone at Plum Creek, 



S.OHIO CENTRAL OHIO N.0HI0 S.MICHIGAN 



Fig. i. — A generalized north-south section through Ohio and southern Michigan, 

 showing the relations of the Olentangy shale and the Prout formation. 



containing at both places pyritized Bactrites arkonensis and Torno- 

 ceras uniangulare, besides Nucula triqueter and Leda rostellaria. 

 Then, too, as Stauffer has shown, the faunas of the Prout limestones 

 of this and of the Encrinal of Ontario are very similar, the latter 

 containing over 75 per cent of the species found in the former. On 

 the whole, therefore, Stauffer's position seems well taken, and we 

 may accept his correlation of the Prout limestone with the "En- 

 crinal" of Thedford and perhaps with the Encrinal (Morse Creek) 

 of western New York. 



We cannot, however, use the name Qlentangy for the shales 

 below these horizons, and therefore the Canadian term "Arkona 

 shales" is preferable. This name may be then applied likewise 

 to the shales of Plum Creek. The comparative study of the 

 brachiopods of these various shales, now in process, will throw 

 further light on the provincial relationships of these formations. 



