It is difficult to institute any minute comparison between the
Atherfield Clay as here developed and the corresponding strata
in the Isle of Wight. It is noteworthy that no specimen was
seen at Dover of the large species of Perna which occur in the
Perna Bed of that district, and it is not unlikely that the junc-
tion here between the Weald Clay and the overlying Aptian beds
does not coincide very strictly in position with the base of the
Lower Greensand in the Isle of Wight. With regard to the
great abundance of Pinna robinaldina at Dover below a depth
of 418 feet, it may be remarked that although this species occurs
in the Perna Bed of the Isle of Wight, yet its particular abun-
dance in the lower part of the clay overlying this was noticed by
Fitton 1 . It is not improbable that the palaeontological dis-
tinction between the Perna Bed, the Atherfield Clay and the
overlying " Crackers " is much less marked than might be sup-
posed from the early published lists of fossils from them, and
at Dover we find some species in the lowest 10 feet of the clay
which were noted by Fitton as making their first appearance in
the Crackers.
