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314 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the Lower Charleton do not find representation in the Esthonian sec- 
tion, since the English Head formation appears younger than the 
Wesenberg and older than any part of the Lyckholm. 
If the views previously expressed ! as to the chronologic position of 
the Ellis Bay formation be correct, it follows that the correlation of 
the Borkholm with the Ellis Bay formation leads to the conclusion 
that the former is not represented in the known deposits of the North 
American Interior. As the Charleton formation is certainly the 
equivalent of the Richmond beds of the Interior, the conclusion follows 
from the above correlation that the Lyckholm beds are of Richmond 
age, and such the writer considers them, referring them with little 
doubt to the upper portion of that formation. It may be noted that 
Bassler correlated the Upper Lyckholm and the Borkholm with the 
Richmond which he considers of early Silurian age. In the latter 
view I can not follow him. 
These two divisions have repeatedly been correlated with the Lep- 
taena kalk and Brachiopod shales of Sweden and the Gastropoden 
kalk and Meristella crassa zone of Norway and I now see no reasons 
for dissenting from this view. Correlation has also been made with 
the Caradoc or Bala of the British Isles, but detailed work is neces- 
sary to determine the exact position. Its closest relations appear to 
be with the Keisley limestone of northwestern England and the Chair 
of Kildare limestone of Ireland. 
THE SILURIAN SYSTEM. 
Introduction. The most easterly observed occurrence of the 
Silurian strata of Esthonia is near the village Pastfer to the north- 
west of Lake Piepus. It thence extends westward, south of Herkiill 
and Hapsal, forming the surface rock of the south end of Dago and 
the whole of Moon and Oesel. On the mainland its outcrop forms a 
strip about 40 miles wide from north to south. 
Except that there is no appreciable departure from parallelism of 
bedding, the stratigraphic relations of the lowermost division of the 
Silurian to the Borkholm formation are not known. At no place was 
the contact with the Ordovician seen. According to Schmidt, a 
contact was formerly visible at Herkiill, but at present there is no 
1 Twenhofel. Loc. cit., 1914. 
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