172 OLDER PLIOCENE PERIOD. 



[Ch.XlII. 



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, vertebrae 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 

 * R, Taylor, Geol,of East Norfolk. 



