TERTIARY FORMATION. 



267 



This deposite contains hydrate of iron, and but few 

 organic remains. 



The second division embraces the plastic clay. 

 This is well exhibited at Gay's Head (Martha's 

 Vineyard), and consists, in general, of interstratified 

 inclined layers of gravel, conglomerates, sands, 

 variegated clays, iron ore, and lignite. These clays 

 and sands are of different colours and texture, and 

 contain shark's teeth, crocodile bones, and other 

 organic remains. 



Some of the remains of a shark were discovered 

 at Gay's Head, which Professor Hitchcock esti- 

 mates to have been from thirty to fifty feet long. 

 This result corresponds with the conclusions of 

 European geologists, that the extinct animals were 

 much larger than those now existing, and that all 

 climates were of a tropical character. The lignite 

 (coal) which occurs in it forms beds sometimes 

 several feet thick, or is mingled with the clay in 

 comminuted dark masses, resembling peat, through 

 which logs are interspersed. Sometimes the woody 

 fibre is very distinct. 



The plastic clay formation, distinguished by inter- 

 stratified lignites with amber, and the relics of ma- 

 rine animals and terrestrial vegetation, lies imme- 

 diately above the green sand formation, which is 

 the equivalent of the chalk of Europe, though want- 

 ing in this country, and extends from Cape Cod to 

 the borders of the Gulf of Mexico. 



In the State of New- York the tertiary formation 

 forms a deposite from the head of Lake Cham plain 

 to its outlet, extending about four miles from the 

 lake on the west side, and from six to twelve miles 

 on the east, interrupted, however, occasionally by 

 primary rocks, which jut up against the lake shore. 

 It forms a bed averaging twenty-five feet thick, 

 composed of clays and sands, and embracing ma- 

 rine shells or relics of a very recent date. The 

 tertiary extends above the level of the lake about 

 200 feet. 



