EARLY SILURIAN ROCKS IN HUDSON BAY REGION | 337 
Pterimea occidentalis, Isochilina grandis var. latimarginata, and 
Leperditia hisingeri var. fabulina. In the Hudson Bay region a zone 
a few feet above the horizon of Virgiana decussata furnished shells 
of Camarotoechia ? winiskensis, Pterinea occidentalis, Isochilina 
grandis var. latimarginata, and Leperditia hisingeri var. fabulina. 
In the northern peninsula of Michigan‘ early Silurian strata con- 
taining Camarotoechia? winiskensis, Isochilina grandis var. lati- 
marginata, and Leperditia hisingeri var. fabulina overlie the strata 
containing Virgiana mayvillensis, which is a near relative of 
Virgiana decussata. In eastern Wisconsin Virgiana mayvillensis 
occurs in the uppermost layers of the Mayville limestone above 
which there is a stratigraphic break, the horizon of Camarotoechia ? 
winiskensis, Isochilina grandis var. latimarginata and Leperditia 
hisingert var. fabulina, present farther east in northern Michigan, 
having been removed by erosion. However, there is no doubt that 
the strata which in northern Michigan contain Virgiana mayvillensis 
correspond in age to those containing the same species in the upper 
part of Mayville limestone in Wisconsin, as they are clearly a north- 
eastward continuation of thesame beds. The relations of the strata 
containing Virgiana to the overlying and underlying beds in the 
regions above described are shown in the columnar sections in Fig. r. 
In Wisconsin there was found in the quarry near Peebles a zone 
only a few feet below the horizon of Virgiana mayvillensis and 
apparently conformable with it, which yielded such characteristic 
Edgewood species of fossils as Dalmanella edgewoodensis, Rhyncho- 
nella ? janea, Rhynchotreta parva, and Atrypa putilla. The position 
of Virgiana mayvillensis in Wisconsin in the upper part of the May- 
ville limestone, which at a slightly lower level contains a character- 
istic Edgewood fauna, indicates that this horizon is Alexandrian 
(late Edgewood) in age. It is also significant that the strata con- 
taining Virgiana mayvillensis in Wisconsin seems to occupy about 
the same position in the Silurian column as do the strata which 
contain Virgiana barrandet in the Becsie River formation of 
Anticosti Island. 
tT. E. Savage and H. F. Crooks, “‘Early Silurian Rocks of the Northern Peninsula 
of Michigan,” Am. Jour. of Science, XLIV (January, 1918), 59-64. In the lists of 
fossils given in this paper the name of the species given as Airypa putilla should have 
been written aff. Atrypa putilla. 
