Vill SUPPLEMENT TO THE CRAG MOLLUSCA. 
In this way it is almost impossible to separate the Red Crag into those chronological divi- 
sions of it that probably exist ; but there are two, besides that of Walton, which may be 
clearly indicated. The first of these is the Red Crag of Butley, in which the northern forms 
of Mollusca predominate, and in which MWucula Cobboldie and the species of Leda 
become very common, and of which the whole fauna, both in individuals and in species, 
makes a great approach to that of the Fluvio-marine Crag, offerimg in this respect a great 
contrast to the Crag of Walton. ‘This approach to the one and contrast with the other 
would, we are convinced, be greatly enhanced could we eliminate from the evidence those 
false witnesses, the intermixed shells derived from older banks swept away. ‘The second 
of these beds needs no special paleeontological test for its distinction, as it rests on the Red 
Crag of Butley, in the section under Chillesford Church (see Section XVII). It consists of 
Crag, gradually losing both the red colour and the oblique bedding as we ascend in the section, 
becoming horizontal in the upper layers. ‘This Crag is poor in species, being largely made 
up of Zellina pretenuis and T. obliqua ; but in it appears Scrobicularia plana in some 
abundance, a shell unknown in the other parts of the Red, but occurring in the Fluvio- 
marine Crag of Bramerton. Valves of Mya truncata also, which are unknown to the 
Walton bed, and almost so to the Crag of the Deben region, but which become common 
in the Butley Crag, are very abundant in these Scrobicularia beds, where exposed 
over the Coralline Crag at Sudbourn in Section X VIIL. 
Although there is doubtless an intermingling of more than one stage of the Red Crag 
in that region which is cut by the rivers Orwell and Deben, it would be impracticable to 
distinguish them further here ; and, accordingly, in the sections all this Crag has been 
grouped under the same symbol as the Crag of Butley, viz. as 4”, although it is probably all, 
or most of it, older than the Butley bed; the still older bed of Walton being distinguished 
by the symbol 4’, and the newest, or Scrobicularia Crag, by 4”. 
Tur CHILLESFoRD BeEps, AND THE CoRRELATION OF THE RED AND FLUVIO-MARINE 
CRAGS. 
Although for the most part they seem to have been swept off the Red Crag region, yet 
we find this Crag capped in a few places by some beds that remain more complete over 
the Fluvio-marine Crag area. ‘These consist of a micaceous sand (5’) in which occurs, 
though not constantly, the shelly bed z. This sand passes up without break into a bed 
of laminated micaceous clay (5”), which, in some localities, yields a few shells, or their 
casts. This bed varies from a dark blue tenacious laminated clay, as at Aldeby and 
geologists must be on their guard against it. A specimen of Tellina obliqua obtained by H. Norton, Esq., 
of Norwich, at Walton, probably got there in this way. In Mr. Wood’s collection in the British Museum 
is a specimen of 7. pretenuis labelled Walton, which he thinks must have originally come from some other 
locality. 
