ART. 21 ORDOVICIAN TRILOBITES ULEICH 57 



the highest of the Blount formations. There can be, therefore, 

 no question concerning the post-Middle Chazyan and pre-Mo- 

 hawkian age of the Telephus-hesirmg beds of the Blount group 

 whose relations to formations with similar fossils in southeastern 

 Canada and Europe we are seeking to establish. 



Blount faunas differ frcwi similar faunae elsewhere. — The for- 

 mations of the Blount group being confined in the Appalachian 

 Valley to troughs with sediments of this age pinching out not only 

 to the west but also in northward direction before reaching the 

 southern boundary of Maryland, there is, as already mentioned, 

 no direct connection between them and Mystic in the southwestern 

 corner of Quebec Province, where highly fossiliferous bowlders of 

 a particular kind contain Telephus Tnystlc&iisis as one of nearly q. 

 hundred mostly undescribed species of the Atlantic fauna of its time. 

 Of these many and varied kinds of fossils none seems strictly iden- 

 tifiable with any of their congeners in Blount formations to the 

 south; and a considerable percentage of the Mystic bowlder fauna 

 has no close relatives in Virginia, Tennessee, or Alabama. A few 

 of the brachiopods, especially the species of Strojphonienaf and 

 Sowerhyella.^ which always are difficult to classify, may on final 

 comparison with Whitesburg limestone species prove insufficiently 

 marked by peculiarities to warrant their separation under distinct 

 names. A few of the trilobites also are closely allied to southern 

 Appalachian species, and others are very near or the same as New 

 foundland species. In fact Raymond-^ indentified some of them 

 with both their southern and Newfoundland allies. Provisionally, 

 I am willing to accept Raymond's judgment regarding most of the 

 latter instances, but in the other cases, after making direct com- 

 parisons of Mystic and Newfoundland specimens with their nearest 

 southern relatives, I must question the validity of his opinion. The 

 observed differences, at least as regards the trilobites, seem in every 

 case as great as those which distinguish the American species from 

 their European allies and which in every case he regarded as 

 demanding specific recognition. 



Reason for observed difference in faunas. — Now, however similar 

 in general aspect these northern and southern Appalachian faunas 

 may be, why do they contain so few specific identities ? I think it is 

 because the beds in which they occur are not strictly of the same 

 ages. In other Avords, those in the St. Lawrence trough were de- 

 posited at times when that part of the geosyncline sank beneath sea 

 level and when its southern part stood above that level. This is not 

 a new and unheard-of conception but merely a new application of 

 views thoroughly discussed and abundantly illustrated by examples 



=" Raymond, P. E., Mus. Comp. Zool. Bull., vol. 67, No. 1, 1925. 



