ART. 21 OEDOVICIAN TKILOBITES ULRICH 59 



ORIGIN AND AGES OF POST-BLOUNT FAUNAS IN NORTH AMERICA 



AND EUROPE 



Post-Blount formations in Anierica. — It is a well established fact 

 that the east Tennessee part of the Appalachian Valley tract con- 

 tains no Ordovician deposits with fossils of either the middle or 

 north Atlantic realms that are younger than the Ottosee. Those 

 that succeed the Ottosee here are all extensions of Ohio, Kentucky, 

 and central Tennessee formations with faunas that invaded from the 

 south. But south of Tennessee, in the Cahaba Valley, in Alabama,^® 

 there is a limestone formation, the Little Oak, with a maximum thick- 

 ness of at least 500 feet, that pinches out in southward direction near 

 Siluria and also in a northerly direction not far beyond Odenville. 

 Near Siluria its thinned southern edge rests on the similarly at- 

 tenuated extremity of the Athens, but greater thicknesses of both 

 occur in the belt between Shelby and Talladega Springs. At and to 

 the north of Pelham the Little Oak rests on the Lenoir, and over 

 most of its outcrop its top is in contact with Devonian or Mississip- 

 pian deposits. 



The Little Oak fauna, even considering only its generic character, 

 has little in common with any of the Blount faunas except that of 

 the Holston. But it does exhibit a general and in part close resem- 

 blance to the Lenoir fauna and through that with the Middle 

 Chazyan fauna in the Champlain Valley. 



South of Harrisburg, Pa., and on through Maryland into Virginia, 

 as far at least as Lexington, there is another limestone formation, 

 named from Chambersburg, Pa., that contains a number of faunules 

 that comprise a considerable percentage of species whose relatives 

 are known elsewhere in America mainly or only in the Little Oak, 

 Ottosee, and Lenoir formations. In southern Pennsylvania the 

 Chambersburg rests on the Lowville, which fixes its age as younger 

 than Lower Black River. But at Lexington, Va., beds that are un- 

 questionaly a largely traced southward extension of it rest on the 

 limestone facies of the Athens. At both places — also at Strasburg 

 and other localities in northern Virginia and in Maryland — the 

 Chambersburg is followed by Martinsburg shale which begins with 

 the shaly facies of the Lower Trenton. Locally, however, as at 

 Chambersburg, a few feet of shaly limestone, with recurrent middle 

 Atlantic trilobites, intervene. 



We have then two post-Blount formations in the Appalachian Val- 

 ley — one under the Lowville, the other over it — the faunas of which 

 agree in general aspect and in containing at least a few generic types 

 that are believed to be indigenes of the middle Atlantic realm whose 

 purer Ordovician fauna is so well represented in the TelephiLS-hesir- 



28 See Butts, Charles, Geology of Alabama, p. 112. 1926. 



