Plastic Clay. 



185 



colored by the red oxide of iron, and forms an important part of the 

 cliff 3. Red and White Clay. This is a mixture of the two first 

 varieties, and the two colors being often fantastically arranged, give 

 to the cliffs a gay appearance. 4. Bluish Gray Plastic Clay. This 

 is the most compact of all the varieties. It often becomes nearly 

 black, where it lies contiguous to the beds of lignite: and when in 

 contact with the white and red varieties, a mixture of them all re- 

 sults. 



2. Sands. Next to the clays the sands are most abundant : though 

 at Gay Head they do not exist in great quantity. They are there 

 sometimes interstratified with the clays ; and indeed, some varieties 

 of the clay contain so large a proportion of sand, that it is not easy 

 to determine whether they should be denominated clays or sands. 

 Of the sands I have noticed the following varieties. 1. White Sili- 

 ceous Sand; generally fine, but sometimes coarse. This is the vari- 

 ety which is spread over almost every part of the southeastern dis- 

 trict of New England ; generally, however, mixed with pebbles and 

 bowlders, and constituting diluvium. It may be seen in its greatest 

 purity near the extremity of Cape Cod ; where it is of snowy white- 

 ness ; and also on Nantucket. On the Vineyard it is generally yel- 

 lowish from the oxide of iron. 2. The same sand, cemented by the 

 yellow hydrate of iron, so as to form a loose sandstone. It is easily 

 crumbled down, however, and is not abundant. I have noticed it at 

 Gay Head ; in the cliff in the eastern part of Chilmark ; and on 

 Nantucket, a mile northwest of the town. 3. White Micaceous Sand. 

 This is in fact a mixture of silex, mica, and white clay ; the latter 

 ingredient not being present in sufficient quantity to hold the particles 

 together. Not abundant. 4. Green Sand ; of a distinct but dull 

 green color. It is sometimes so mixed with clay, as to form a com- 

 pact mass, even when dry. It is interstratified with the red and white 

 clays at Gay Head, where alone ha ve I noticed it. It is this stratum 

 that contains the greatest variety of the organic remains at Gay 

 Head ; and on this account, its exact geological position is important 

 to be known. It has been already remarked, that the strata in this 

 cliff dip nearly north, or rather a little inclining to the northeast, at 

 an angle varying between 20° and 45°. Now the green sand lies 

 near the northern extremity of the cliff, through it is succeeded by 

 other strata of the same clays that constitute the principal part of the 

 cliff Hence we may infer that the green sand lies near the upper 

 part of this formation, so far as we can judge from this cliff : though, 

 24 



