60 
mussel, periwinkle, and Scrobiculciria piper ata. Adjacent to, 
and resting upon, this yellow clay occurs a very liard dense 
black mud, difficult to break down and which when heated and 
suddenly cooled in water gives off a strong volume of 
sulphuretted hydrogen, the residue when washed containing 
much vegetable matter, probably seaweed, of which I find 
several species too far gone for accurate determination. A 
few seeds of land plants, Ranunculus repens , Rubiis fruticosm 
and Rhinanthus c rising alii , and fragments of Coleoptera are 
occasionally met with. 
In this horizon derived Eocene forms are not uncommon 
but are easily distinguished from the more recent types by 
their colour, or the greenish gray sand in their cavities. In 
the absence of these indications, considering the affinities of 
the fauna of the mud deposit which will appear further on, it 
is difficult to determine in the case of such genera as Leda, 
Cardita, Area, &c., whether they are derivative or not, the 
specific differences being like the individual, small, between 
the Eocene and later forms. 
The Foraminifera are also of somewhat uncertain age, but 
as a rule the larger hard mud species are such Eocene forms as 
Nummulites, Discorbina, and Alveolina, these constituting the 
principal genera. 
Fish Otoliths are common but are probably of the same 
origin, although some of them are very much fresher than 
others in appearance. 
The intervening space is filled with a fine silty sand, the 
present width not extending above 150 to 200 yards, the 
higher and wider spreading portions of the deposit having 
been bodily removed. How thick this bed was originally 
there are no means of ascertaining, but as the present level of 
the silt bed is 4 feet below that of the Pholades which are full 
of the debris, it was probably much more extensive and 
widely developed. This area is replete with mollusca in their 
original positions, the interior of the larger bivalves abounding 
in the most delicate molluscs, hydroids and polyzoa in exquisite 
preservation. 
The entire group of deposits rests upon a freshwater gravel, 
and there is no evidence, indeed it is almost a certainty, that 
