124 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
turbing because it leads to a correlation that is in distinct conflict with that indi- 
cated by other groups of animals. 
The Viola limestone is commonly a light-gray to dark-buff limestone, but it 
may be nearly white with scattered brown blotches. The limestone is usually 
tough, fine-grained, but some coarsely crystalline beds occur in it. At Rock 
Crossing in the Criner Hills a shaly zone occurs at the base, but a similar shaly 
zone occurs elsewhere 100 to 150 feet above the base. The limestone is mostly 
thin bedded in layers 2 to 6 inches thick. The formation, minus the Upper Ordo- 
vician (Fernvale), attains a thickness of 165 to 880 feet. 
The Viola formation has been dated as spanning the time of Trenton to Rich- 
mond sedimentation. The Upper Ordovician has been separated as the Fernvale 
formation. The only part of the Viola of immediate concern in this discussion is 
the lower part and that of the shales. Brachiopods reported from the lower mem- 
ber of the Viola according to Decker (1933, p. 1414) are: 
*Dalmanella hamburgensis *Rafinesquina deltoidea 
Dinorthis pectinella *Rhychotrema increbescens 
Paterula polita Cooper *Strophomena filitexta 
Platystrophia sp. *Zygospira recurvirostris 
*Plectambomites sericeus 
Examination of this list will at once disclose that some of the names are prob- 
ably incorrect. The combination of species does not exist anywhere else and 
seems impossible from what is known of Trenton faunas elsewhere. The list, 
however, is sufficiently accurate to show that the assemblage belongs above the 
lower Trenton. The presence of Dinorthis pectinella suggests the Ion member 
of the Decorah formation, but the reported presence of Platystrophia makes 
further complications. This genus does not appear below the Trenton as far as 
present knowledge goes. Furthermore, it is not known in low Trenton but char- 
acterizes Hull in New York and Ontario and the Prosser in the upper Mississippi 
Valley. 
On the basis of brachiopods, therefore, the lower Viola would be placed at the 
lowest with about middle Trenton. Decker (1952, p. 100) makes the same age 
assignment for the Viola. Inconsistent with this age, however, is Decker’s (1952, 
p. 101) reported discovery of the Nemagraptus fauna in the lower part of the 
Viola. The occurrence of the trilobite Robergia in the Viola and its presence in 
the “Athens” (Liberty Hall) led Decker to correlate these two divisions of rock. 
It might be suggested here that an inconsistency exists with the trilobite and 
perhaps also with the graptolite. In the Appalachians the Nemagraptus fauna is 
the midgraptolite zone of the Athens at the Athens type locality, as in other parts 
of the Appalachians. It has been shown above that type Athens is equivalent to 
the Arline formation. In Catawba Valley the Nemagraptus fauna occurs 300 feet 
above Botetourt—Effna formations which are equivalent to part of the Arline. 
Now the Arline fauna is many hundreds of feet below the Oranda or overlying 
Salona faunas, which are the only ones in the Appalachian Valley that could be 
correlated with the lower Viola brachiopods listed above. Thus Nemagraptus in 
the Appalachians is definitely below Oranda—Salona faunas. However, the 
