INTRODUCTION. XVI 
sands, extremely rare, and as we get no trace of it in later beds it was evidently then 
dying out. 
There is one species, however, which comes in with these beds that is wholly unknown 
in any older ones, and is especially characteristic of every Glacial and Post Glacial deposit, 
viz. Tellina Balthica (Psammobia solidula). It has been objected that the occurrence of 
this shell at Weybourn is due to geographical causes, and that notwithstanding its 
presence there, some part of the Crag is comprised in the section at that place (No. IV) ; 
but apart from the fact that there is nothing at Weybourn answering physically to the 
Chillesford clay,’ the Glacial, and non-Crag age, of this shell is proved by its absence from 
every exposure of sand (and they are many) that can be proved to belong to the Crag 
series by having the Chillesford clay over it; industriously as these beds have, many of 
them for half a century, been searched by collectors. Such Crag beds range up to within 
twelve miles of the Weybourn Cliff, occurring at Coltishall, Horstead, and Burgh, (see 
Sections 1X, X, and XI) and in the neighbourhood of Coltishall and Horstead they are 
in the immediate contiguity of the pebbly sands with Zellina Balthica. hus while, in 
every bed of this neighbourhood which can be proved to belong to the Crag by having 
the Chillesford clay over it, not a trace occurs of this shell, several fossiliferous sections of 
the Lower Glacial sands resting direct on the chalk are to be found im the immediate 
neighbourhood of such proved Crag beds; and these swarm with JZe/lina Balthica. 
Pits of the sands thus swarming with this shell occur at Belaugh (see Section N), only 
eight and eleven furlongs respectively from the well-known pit at Coltishall (No. X), 
and about three furlongs further from the equally well-known pit at Horstead (No. XJ), 
in both of which the sands 5’, full of shells, are exposed with the Chillesford clay over 
them, but in which sands no trace of this shell, as before observed, has been detected. 
No impartial observer can, we think, doubt that such Ze/lina Balthica sands are those ot 
the Lower Glacial formation, resting direct on the chalk in spaces from which the Chilles- 
ford beds have been previously denuded. It is only near the chalk floor that Mollusca 
usually occur in these beds, though where they overlie the freshwater bed C at Woman 
Hythe (Sections W and III) there occurs in them high up, where they are interbedded 
with the Till, a colony of Mya truncata double, and with siphonal ends uppermost, as 
they lived. We took from these sands at Weybourn part of a mammalian humerus. 
Where these sands pass into shingle masses, we evidently approach the shore of the 
sea of their period, while where they are obliquely bedded in deep sections, we find its 
actual beach line. ‘Tracing them from these parts towards the north Norfolk coast, and 
observing the way they are overlain by the contorted drift, where the Cromer Till is not 
present, as well as the the special characters of that drift, we find the Till (6a) to be 
merely the deeper water deposit of this early Glacial estuary, in which these shingle 
1 A few inches, or sometimes a foot, or little more, of gray clay over the large flints which rest on the 
chalk, and among which shells are interbedded, can, we think, never be mistaken for so well-defined a 
formation as the Chillesford. 
d 
