CORALLINE CRAG. 
23 
Next year appeared Prof. Prestwich’s important series of 
papers on the structure of the Crag beds.* The first of these— 
that on the Coralline Crag of Suffolk—had been read before the 
Geological Society in 1868 and is several times alluded to in 
Prof. Lankester’s paper published somewhat later in that year. 
Prof. Prestwich gave full details of the different Coralline Crag 
pits, adding a map of the outlier at Sutton and levelled sections 
across the hill. He concluded that several zones could be traced 
in the Coralline Crag, though the higher ones sometimes overlap 
the lower so as to rest on the London Clay. The total thickness 
was taken to be about 76 feet, and in a generalized section the 
following divisions were made :— 
Feet. 
Upper Division, 
36 feet. 
Lower Division, 
47 feet. 
In a later paper a slight correction is made—It is possible 
that the estimate for bed may be 2 feet, and for bed * 
5 feet, too thick, which would make the thickness of the lower 
division of the Coralline Crag about 40 instead of 47 feet.” 
Under the heading General Considerations ” Prof. Prestwich 
gives an account of the history of the Older Pliocene strata, and 
of the physical changes which took place in the Anglo-Belgian 
basin during the Miocene and Pliocene periods. He then points 
to the varying conditions under which the different portions of 
the Coralline Crag were deposited, and traces the changes 
indicated by the beds overlying the Nodule Bed thus : As the 
land subsided the coarser materials of the basement-bed were 
covered up by a bed of comminuted shells. This subsidence 
continuing, beds ^ c ’ and ^ d ’ were deposited in comparatively 
deep and tranquil water. These beds are succeeded by the sands 
" abounding in Bryozoa, with small Echini, and a number of 
small bivalves, indicating apparently the greatest depth of sea 
(possibly of from 500 to 1,000 feet) attained during the Coralline- 
Crag period. A change then took place, and a bed of comminuted 
* Quart. Journ. Geol. Soc., vol. xxvii. pp. 115-146. 
f h. Sand and comminuted shells - - 6 
'l g. A series of beds consisting almost entirely") 
j of comminuted shells and remains of | 
Bryozoa, forming a soft building-stone. )>30 
False stratification and oblique bedding 
are its constant characters - -J 
Sand with numerous entire small shells and ) ^ 
seams of comminuted shells - - / 
e. Sands with numerous Bryozoa, often in the ] 
original position of growth, and some 112 
small shells and Echini - - - J 
d. Comminuted shells, large entire or double ] 
shells, and bands of limestone in the V15 
upper part - - - - - J 
c. Marly beds with numerous well-preserved] 
and double shells, often in the position in 110 
which they lived - - - - J 
b. Comminuted shells, Cetacean remains,) . 
Bryozoa - - - - - J 
a. Phosphatic nodules and mammalian remains 1 
