TERTIARY FORMATION. 
265 
sippi, occupying a surface of from 200 to 500 miles 
broad, and extending, in all probability, west of the 
Mississippi to the foot of the Rocky Mountains, We 
find it commencing near the head of Lake Cham- 
plain, skirting the east side of the lake, seldom ex- 
tending over half a mile from the edge of the water, 
containing shells and flints. When it reaches the 
south extremity of the lake near Whitehall, it 
spreads out across the northern point of the state 
of New-York, striking the head of Lake Ontario at 
the Thousand Islands, and spreading over the whole 
of Western New- York, and Western Pennsylvania 
and Virginia, and occupying the whole surface of 
the Middle, Western, and Southern states. It also 
occupies that belt in the Connecticut Valley and 
along the Atlantic coast which we have described 
as belonging to the new red sandstone ; also the 
green sand and cretaceous groups. 
CHAPTER XXVI. 
TERTIARY FORMATION. 
Superior Order (Conybeare). Supracretaceous Group 
(De la Beche). 
Tertiary.— How distinguished from other Formations? — Mr* 
Lyeil's Division— Pliocene, &c. — Its Range and Distribu-^ 
tion. — Professor Hitchcock's Arrangement. — Plastic Clay.— » 
Tertiary in State of New-York. — Ancient Arm of the Sea.—* 
How Drained. — Newer Pliocene of the United States.-^ 
Older Pliocene and Miocene Formations of the United 
State. — Eocene do. 
This group has but lately been erected into a dis- 
tinct formation, as the strata assigned to it were so 
loosely aggregated that they were supposed to be 
of modern origin, and, in fact, merely alluvial. 
Z 
