WOOLWICH AND READING SERIES. 
267 
Among many characteristic bivalve shells are Leda amyg- 
daloides (Fig. 213) and Cryptodon angulatum (Fig. 214), 
and among the Radiata a Astropecten (Fig. 215). 
These fossils are accompanied by a sword-fish (Tetrapterus 
prisms^ Agassiz), about eight feet long, and a saw-fish {Pris- 
tis bisulcatus^ ^^out ten feet in length; genera now 
foreign to the British seas. On the Avhole, about eighty 
species of fish have been described by M. Agassiz from these 
beds of Sheppey, and they indicate, in his opinion, a warm 
climate. 
In the lower part of the London clay at Kyson, a few 
miles east of Woodbridge, the remains of mammalia have 
been detected. Some of these have been referred by Pro¬ 
fessor Owen to an opossum, and others to the genus Ilyra- 
cotheriurn. The teeth of this last-mentioned pachyderm 
were at first, in 1840, supposed to belong to a monkey, an 
opinion afterwards al3andoned by Owen when more ample 
materials for comj)arison were obtained. 
Woolwich and Reading Series (C. 2, Table, p. 252).—This 
formation was formerly called the Plastic Clay, as it agrees 
Avith a similar clay used in pottery Avhich occupies the same 
position in the French series, and it has been used for the 
like purposes in England.? 
No formations can be more dissimilar, on the Avhole, in 
mineral character than the Eocene deposits of England and 
Paris; those of our own island being almost exclusively of 
mechanical origin—accumulations of mud, sand, and pebbles; 
Avhile in the neii>:hborhood of Paris we find a o’reat succes- 
sion of strata composed of limestones, some of them siliceous, 
and of crystalline gypsum and siliceous sandstone, and some¬ 
times of pure flint used for millstones. Hence it is often im¬ 
possible, as before stated, to institute an exact comparison 
between the various members of the English and French 
series, and to settle their respective ages. But in regard to 
the division which Ave have noAV under consideration, Avheth- 
er AA^e study it in the basins of London, Hampshire, or Paris, 
Ave recognize as a general rule the same mineral character, 
the beds consisting over a large area of mottled clays and 
sand, Avith lignite, and Avith some strata of well-rolled flint 
pebbles, derived from the chalk, varying in size, but occa¬ 
sionally several inches in diameter. These strata may be 
seen in the Isle of Wight in contact with the chalk, or in 
the London basin, at Reading, Blackheath, and Woolwich. 
In some of the loAvest of them, banks of oysters are observed, 
consisting of Ostrea bellovacina^ so common in France in the 
* Prestwich, Quart. Geol. Journ., vol. x. 
