Geology of Martha’s Vineyard. 245 
low. The ferruginous pebble beds are brown, or reddish, 
sometimes a deep blood red, and they are generally ce- 
a 
require a considerable blow of the hammer to separate the 
fragments. This is particularly the case in the lower part 
of these strata ; where the iron ore, which appears to be the 
argillaceous, is sufficiently pure to be wroaght, although 
penetrated by pebbles throughout. Some of the clay beds 
are nearly half made up of small plates of silver coloured 
mica, intimately mixed with the clay, which appears to be 
kaolin. In this clay, beneath the ferruginous pebble beds, 
! found good specimens of well characterised lignite.” It 
consists of flattened trunks, or branches, several inches in 
diameter, of a clove brown colour, retaining, very distinct- 
ly, its longitudinal, fibrous structure: but the cross fracture 
's conchoidal and shining, and the concentric rings are in- 
visible. The bark isa mere line in thickness. It burns 
without much difficulty, with considerable flame, and emits 
a pungent rather unpleasant odour. It lies horizontal in 
some 
upwards, and in others they arch downwards. Whether 
this irregularity does not proceed from a partial sliding 
Thane masses of the cliff, I could not determine ; 
though inclined to believe it doesnot. 
_ The above description, it will be perceived, conennsoes 
in its general characters, to the Kuropean Plastic - y 
Fo ion ; and therefore the strata it embraces have been 
thus denominated. But in order to establish their identity 
with perfect certainty, a comparison must be oo ga - 
tween the organic remains, occurring 1! eac rae 
strata. It is not therefore, without some doubt, ae ave 
denominated the formation, above described, the Plastic 
