172 
OLDER PLIOCENE PERIOD. 
[Ch. XIII. 
consist of sand, gravel, and blue or brown marl— the shells 
imbedded in the sand and marl being, for the most part, broken 
and sometimes finely comminuted. In a few spots we find the 
deposit in the form of a soft stratified rock, composed almost 
entirely of corals, sponges, and echini* an assemblage of 
species which probably lived in a tranquil sea of some depth. 
In other parts of our coast it consists of alternations of sand 
and shingle, destitute of organic remains, and more than 200 
feet in thickness, as in the Suffolk cliffs, between Dunwich and 
Yarmouth. In others, we meet with an enormous mass, more 
than 300 feet in thickness, of sand, loam, and clay, containing 
bones of terrestrial quadrupeds and drift wood, sometimes stra- 
tified regularly, at others consisting of a confused heap of 
rubbish, in which fragments of the chalk and its flints are im- 
bedded in a chalky marl. 
In this aggregate are also found many fragments of older 
rocks, the septaria of the London clay, together with ammo- 
nites, vertebra? of ichthyosauri, and other fossils from parts of 
the oolitic series. It has been questioned whether all the 
above-mentioned beds can be considered as belonging to the 
same era. The subject may admit of doubt, but after exa- 
mining, in 1829, the whole line of coast of Essex, Suffolk, and 
Norfolk, I found it impossible to draw any line of separation 
between the different groups. Each seemed in its turn to pass 
into another, and those masses which approach in character to 
alluvium, and contain the remains of terrestrial quadrupeds, 
are occasionally intermixed with the strata of the crag. 
There are, however, lacustrine deposits overlying the crag, 
which probably belong to a distinct zoological period. These 
are found in small cavities, which must have existed on the 
surface of the crag after its elevation, and which formed small 
lakes or ponds wherein recent fresh-water testacea were in- 
cluded in loamy strata. (See wood-cut, No. 30, c.) 
Relative position. — The crag is seen to rest on the chalk and 
on the London clay, but usually on the former. The strata 
* Ei Taylor, Geo], of East Norfolk. 
