in America and Europe. 275 
in the South Mountain range in southern Pennsylvania. The 
stratified petrosilex rocks of all these regions were described in 
a communication to this Association, in 1876, as apparently 
corresponding to the Adilleflinta rocks of Sweden, and, having 
n view their stratigraphical position both in that country and 
in New Brunswick, they were then “provisionally referred ” 
“toa position near the base of the Huronian series.” Their 
absence in the Huronian belt in western New England, and in 
the province of Quebec, as well as at several observed points 
of contact between the Laurentian and the well-defined Huro- 
of 
described, it includes, as already said, a basal granitoid gneiss 
Without limestones, which the writer has elsewhere designated 
the Ottawa neiss, and of which the thickness 1s necessarily 
Weertain. apes i this is the Grenville series of Logan, 
