of the United States. 35 



^nd, pebbles and lignite render it easy to distinguish it. At 

 the same time it may be considered as the most important 

 of the tertiary formations, on account of its use in the arts. 



It was first discovered in France, but is peculiarly prom- 

 inent, and finely illustrated in England, at Alum bay in the 

 Isle of Wight, where from some unknown cause, the stra- 

 ta have assumed a vertical position, and the sea washing 

 the face of the cliffs has presented a fine section to the 

 Geologist. 



In England the plastic clay is, I believe, found only in 

 this formation, but in France, a bed of white clay and sand 

 accompanies some of the higher formations. It must re- 

 main for future observations to ascertain whether some of 

 the white plastic clays of America belong to the higher or 

 lower formations, I am inclined to think that most of the 

 American clays are contemporaneous with the English 

 plastic clay and lower French strata, but it is a point which 

 must be decided at a future time, when the exact order and 

 position of these formations is known in America. 



This formation is the most extensive of the tertiary strata 

 in the United States, and presents an important feature in 

 its Geology ; it may be traced at different points nearly ta 

 the distance of a thousand miles. The following are some 

 of the localities where it occurs. 



The situation where it may be studied with the greatest 

 advantage and where it is exhibited in greater perfection 

 than in any other partof the United States, isat Gay Head, on 

 the island sometimes called Martha's Vineyard in Mass* 

 The cliffs are two hundred feet in height, and consist of a 

 succession of beds of clay, sand, ochres and lignite of the 

 brightest hues, and the waves of the ocean which flow at 

 the foot of the hill are tinged by the coloring matter of the 

 sands and clays. I am informed by a gentleman of Phila- 

 delphia, who has visited this place, that amber has been 

 found floating in the ocean, near, undoubtedly derived from 

 the lignite of this formation, and I have a specimen of it in 

 my collection. 



At Sand's Point upon Long-Island, it is very conspicu- 

 ous, consisting of beds of very white clay and fossil wood. 

 The range of hills which extend through the centre of this 

 island, are composed of diluvial sand, gravel, &c. accom- 

 panied by enormous masses of rolled pebbles and bowlders. 



