50 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



in the Girvan District only in and perhaps above the Whitehouse 

 group, which succeeds the Balclatchie, whereas in America the genus 

 is confined to the Athens shale, which succeeds the Whitesburg. How- 

 ever, after seeing the concerned beds in Scotland and reconsidera- 

 tion of the evidence in the light of personal observation of facts not 

 previously available to me, the suggested correlation of the Balclatchie 

 and Whitesburg has become quite impossible. In fact, nothing is left 

 of it than the conviction that the faunas of the two formations were 

 derived from the same Middle Atlantic realm. But they did not re- 

 ceive them at the same time, the Balclatchie invasion of Scotland hav- 

 ing occurred long subsequent to the Whitesburg, and after consider- 

 able modification and change of the earlier composition of the Middle 

 Atlantic fauna had been introduced. The probable truth of this 

 statement is rather plainly indicated by the fact that not a single 

 species has been found in either formation that is strictly the same as 

 any in the other. Also by the fact that the Balclatcliie fauna includes 

 many types that are unknown in Appalachian faunas that contain 

 species of Middle Atlantic origin and are of older dates than the 

 Ottosee, Little Oak, and Chambersburg faunas. The latter fact thus 

 tends to confirm the conclusion that is more satisfactorily substanti- 

 ated by considerations about to be presented. 



In the first place, the lower age limit of the Balclatchie may be 

 said to be conclusively fixed — at least in the minds of British geolo^ 

 gists who rely so strongly in their Lower Paleozoic correlations on 

 the evidence of graptolites — by the fact that it is underlain by a shaly 

 zone that contains Glenkiln graptolites. The Glenkiln, as all agree, 

 represents the Normanskill and Athens shales of the Appalachian 

 geosyncline. It follows, then, that the Balclatchie is not only younger 

 than the Whitesburg but also younger than the Athens. Following 

 this conclusion it seemed at first that the Balclatchie might be cor- 

 related with our Tellico. This correlation found considerable sup- 

 port in the similarity of the pelecypodan parts of the faunas of the 

 two formations; but again the entire lack of specific identities casts 

 doubt on its validity. Besides, the numerous brachiopods of the Bal- 

 clatchie include many species that not only look younger than Tellico 

 representatives of the class but indicate a stronger commingling of 

 northern and Middle Atlantic types than we have reason to believe 

 occurred before the close of Blount time. I may mention, too, that 

 the inconspicuous development of the glabellar furrows and the pres- 

 ence of a nucal spine in the Balclatchie Trinucleus suhradiatits Reed 

 suggests a CryptoUthus rather than a Tretaspis, to which genus it is 

 referred by Stetson.^^ Similar species occur in America only above 

 the Chazyan. 



2^ stetson, H. C, The distribution and relationships of the Trinucleidss : Harvard 

 Coll. Mus. Comp. Zool. Bull., vol. 78, No. 2, p. 88, 1927. 



