452 A POPULAR EXPOSITION OF THE 
References to Map on preceding page. 
No. 18. 
Erie Group. 
Grand River 14.. 
Group 
12. 
Niagara or Anti- 11. 
costs Group. 10. 
9. 
8. 
Ontario Group. 7. 
6. 
Quebec Group. A 
Potsdam G(inpart.) 3. 
oe 2. 
Azoic Group. 7 
Devonian Serres: 
Portage and Chemung Group, (Kettle Point Form.) 
Hamilton (or Lambton) Formation. 
Corniferous Formation. 
Oriskany Formation. 
UprerR SILURIAN SERIRS: 
Eurypterus Formation, or Lower Helderberg Group 
Onondaga or Gypsiferous Formation. 
MippLp SILuRIAN SERIES: 
Guelph Formation. 
Niagara Formation. 
Clinton Formation. 
Medina Formation. 
Lower Sinurian Series: 
Hudson River Formation. 
Utica Formation. 
Trenton (including Bird’s Eye and Black River) Fn. 
Chazy Formation, 
Calciferous Formation. 
Potsdam Formation. 
Azoic Serins: 
Huronian Formation. 
Laurentian Formation. 
