PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 13 
Correlation of Long Point series.—The listed fossils suggested a Trenton age 
for the Long Point series. Glyptorthis bellarugosa, Rafinesquina trentonensis, 
Dinorthis aff. D. iphigenia, and Triplecia extans are now regarded as good indi- 
cators of the Rockland formation or Upper Wilderness stage or possibly slightly 
higher in the Trenton. Valcourea sp. is the only brachiopod listed that is not 
in harmony with a Trenton age, but this one may not be correctly identified. 
COW HEAD BRECCIA 
The Long Point series is overlain by the Cow Head breccia of uncertain thick- 
ness, ranging from 350 feet to probably more than 1,200 feet. This formation 
consists of a mass of ragged blocks of enormous size and of several different 
ages. No fossils have been taken from the matrix of the breccia, consequently a 
definite age is not known. The blocks incorporated in the mass range in age from 
late Cambrian to those of the Long Point series. The formation is thus definitely 
younger than the Long Point. 
HUMBER ARM SERIES 
The Cow Head breccia is overlain by 2,700 feet of red, green, and black shales 
of the Humber Arm series. The few graptolites and brachiopods, among them 
Paterula amii Schuchert, found in the series are thought to be no younger than 
medial Ordovician. However, Schuchert and Dunbar (1934, p. 98) conclude 
that some late Ordovician may be present because of the enormous thickness of 
the series. 
2. ST. LAWRENCE AND OTTAWA VALLEYS AND ADJACENT AREAS 
Areas of Ordovician rock exposure, including the stratigraphic interval em- 
braced by this study, appear in seven general areas: The Mingan Islands in 
the St. Lawrence River north of the west end of Anticosti Island ; Quebec City; 
Montreal; along the Ottawa River in the vicinity of Ottawa and Hull; at the 
head of the St. Lawrence Valley in New York and adjacent Canada; the sec- 
tion at Coboconk, Ontario; and Manitoulin Island region on the north side of 
Lake Huron in Ontario. 
MINGAN ISLANDS 
These islands form a group in the St. Lawrence River just north of the west 
half of Anticosti Island. A sequence of Chazyan rocks called the “Mingan 
formation” has long been known on these islands. 
Mingan formation.—The maximum thickness of this formation is 155 feet, 
according to Twenhofel (1938, p. 23) who described it in detail. The upper 116 
feet are composed of limestone containing numerous fossils. Below these lime- 
stones occur 20 feet of shale with some beds of quartzite and lime sands. The 
basal 3 to 8 feet is composed of sandstone and conglomerate. Fossils occur in 
