AHT. 21 ORDOVICIAN TEILOBITES — ULEICH 85 



of the species listed as common to the Balclatchie and the Craighead 

 limestone. The latter, of course, is referred by him to the Stinchar, 

 and its fossils are listed under that heading. Comparison of Keed's 

 lists therefore indicates a much greater similarity in the fossil con- 

 tents of the Stinchar and Balclatchie formations than is warranted 

 by the facts. Indeed, I am confident that revision and correction of 

 the lists will show that not a single species of the true Stinchar passes 

 upward into the Balclatchie. 



Evidently the Craighead fauna comprises a large proportion — ap- 

 proximately 40 per cent — of derivatives of Balclatchie species. Many 

 of these may be very close relatives that as preserved are not readily 

 distinguishable from their ancestor^. However, experience shows 

 that with good and abundant material and closer attention to details 

 of structure these difficulties of discrimination will become much less 

 and in most instances quite ordinary. Moreover, this similarity of 

 faunas is precisely what should be expected and what we are experi- 

 encing over and over again in comparing faunas that invaded from 

 the same sea at more or less widely different times. 



The Balclatchie, despite the mentioned faunal similarity to the 

 Craighead, is unquestionably Ordovician in age. The only question 

 is how far beneath the top of the American development of the system 

 does it belong? In my opinion the Balclatchie, together with the 

 Benan conglomerate which I regard as the initial deposit of its time, 

 is not older than the Tellico of east Tennessee and both most prob- 

 ably are entirely post-Blount age. The Ardwell Group then may bo 

 placed near the middle of the Black River Group. I have recently 

 procured what seems good faunal and physical evidence for this view 

 in northern Virginia, but more field work and further study of the 

 fossil collections is desired before I shall feel prepared to discuss the 

 problem. 



In the case of the Whitehouse group positive faunal evidence 

 tending to show its stratigi-aphic relations to Appalachian forma- 

 tions is as yet scant and far from conclusive. However, taking into 

 account all of the faunal similarities now suposed to have any bear- 

 ing on the question together with probabilities suggested by the lithic 

 character of underlying and overlying formations in Girvan, we may 

 be safe in placing the Whitehouse within the limits of the Trenton 

 group or perhaps at the contact of the Trenton and Eden groups. 

 After this disposal of the Whitehouse and the more confident refer- 

 ence of the Drummuck to the Medinan the intervening Barren flag- 

 stones seem to fall very naturally into the space occupied in America 

 by the Upper Cincinnatian (Maysville group). The Girvan beds 

 supposed to be of this age agree particularly well with the upper 

 part of the Pulaski group and the Oswego sandstone as developed 

 in parts of New York and Pennsylvania. 



