Cambrian (with Huronian ?).
"The Ancient Life History of the Earth" by Henry Alleyne Nicholson
The Huronian was first recognised by Sir W. E. Logan in Canada, but corresponding rocks exist in Europe.
"The Chain of Life in Geological Time" by Sir J. William Dawson
Hardly less than a dozen of these are now known, ranging in age from Huronian to Eocene.
"Climatic Changes" by Ellsworth Huntington
There is abundant evidence that the subsidence which let the Potsdam seas in over the eroded surface of the Huronian quartzite was gradual.
"The Geography of the Region about Devils Lake and the Dalles of the Wisconsin" by Rollin D. Salisbury