TERTIARY POBMATlOfJ. 265 



sippi, occupying a surface of from ^00 to 6Q0 laSJes 

 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 Chajji- 

 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. 

 Lyell'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. 



