230 AMADEUS W. GRABAU 
to northern Europe (see Fig. 8}. Within the protected interior 
sea, limestones (Upper Stones River and Black River) accumulated. 
Limestones accumulated also along the shores of Laurentia (Canadian 
shield) in the St. Lawrence channel, the two types of sediment and 
faunas thus occurring side by side. There is no need for postulating 
a dividing ridge in this channel, for the faunas and sedimentation 
would remain different as long as the different physical conditions. 
persisted. 
In Great Britain and elsewhere in Europe the zone of Coeno- 
graptus gracilis forms the summit of the Middle Ordovicic. The 
next succeeding zone (Hartfell shales of the Moffat district) is of 
Upper Ordovicic or Caradocian age. This begins with the zone of 
Dicranogra ptus clingani, which in North America is represented by 
the Magog shales or Diplograptus amplexicaulis zone, which succeeds. 
the Normanskill beds. 
The diastrophic movement, which in North America resulted in 
the emergence of most of the continent at the end of Lower Ordo- 
vicic time, was likewise marked, though to a less extent, in Europe. 
Lamansky has recently shown! that between Baltic Port and the 
banks of the river Volkov, the Lower Ordovicic beds (Etage B) 
show the progressive off-lapping structure characteristic of a retreatal 
or beveled-off series of sediments. At Baltic Port only the Mega- 
laspis planilimbata zone (BIla) occurs. Farther east, at Reval, 
the higher Asaphus bréggeri zone (BIIP) and a part of the Asaphus 
lepidurus zone (BIly) have appeared. In the extreme east of the 
gouvernement of St. Petersburg, on the Volkov, the whole of BIly, 
and the Asaphus expansus zone (BIIla) have come in above the 
others. The line of disconformity and erosion is marked by slight 
irregularities, by glauconite, iron oxide, and phosphate concretions, 
rarely by siliceous sediments. Above the erosion plane, the beds 
of BIII8 and BIIIy (zones with Asaphus raniceps and Asaphus 
eichwaldi) show progressive overlapping, the latter being repre- 
sented only by clastic material at Baltic Port. Above these lies the 
Echinosphaerites limestone C, which shows continued westward 
overlapping. 
1 Lamansky, W., “Die 4ltesten silurischen Schichten Russlands,”’ Mém. du. 
Comité Geol., N. S., Livr. XX, 1905. 
