80 Canadian Record of Science. 
are in actual contact; yet we do not know that in either of 
these islands there it any mingling of the two faunas. In 
the St. Lawrence Valley and Gulf, the Georgian Series is 
present at several localities, but no trace of the Acadian has 
been found. These conditions seem to indicate that the 
two series are entirely independent of each other, in which 
case the Georgian would be the more recent. 
But if there is no overlap, as would appear from these 
conditions, then the Georgian can be of no greater antiquity 
than the Ceratopyge beds, and the 4,800 feet of Middle and 
Upper Cambrian in the Hureka district west of the Rocky 
Mountains, would be represented by the 1,000 of the Tre- 
madoc Group in Wales, or the very much thinner Cerato- 
pyge beds of Sweden. 
SERIES D. 
Of the relation of the Potsdam Series to the Georgian 
there is less doubt than hangs around the connection of the 
latter with the Acadian Series. Mr. Walcott’s fortunate 
discovery of the highest bed of this series in the Saratoga 
limestone, has enabled him to show its equivalency to the 
highest Cambrian sandstone in Wisconsin. This group, 
characterized by the genus Dikellocephalus of Owen, ap- 
pears to be equivalent to the Ceratopyge limestone, or the 
Tremadoe Group, and would represent the upper part of 
the Tremadoc, as the Georgian Series probably does the 
lower. 
This, the upper, or true Potsdam, appears to form in 
Eastern North America a fourth series of the Cambrian 
system, since its distribution is not coincident with that of 
the Series C.,, but it is apparently wanting in the region to 
which this article relates. The Potsdam series is present in 
the upper part of the St. Lawrence Valley, and in the 
middle and Western States, but absent, as far as known, 
from the eastern border of the continent. 
In Eastern North America, then, the Cambrian System 
is represented by the following series ;— 
