LOWER CHALK —DEVONSHIRE. 
131 
the interstices. Of this quartziferous chalk (C) with phosphatic 
fossils and nodules there is about 6 inches, and it is directly over- 
lain by hard, yellowish, gritty chalk with fossils of Middle Chalk 
species. The following diagram shows the variation in the thick¬ 
ness of the beds seen in the fallen blocks : — 
Humble 
Point . Blocks Blocks 
Blocks 
Wat er fall 
Pink ay 
Fig 32. Diagram of the variations in the thickness of the 
Cenomanian Beds near Pinhay. 
Of these three beds, A and B form the zone of Ammonites Man- 
telli. Bed A contains many Sponges and Bryozoa, Rhynchonella 
dimidiata (large), Catopygus columbarius, Holaster altus, Pecten 
asper, Trigonia Meyeri, Am. [Acanthi] Mantelli, Am. [Schloen.] 
varians, Am. [ Placenticeras ] largilliertianus Turrilites tubercu- 
latus, and, what is rare in this bed, a specimen of Scaphites 
cequalis. Bed B contains some of the same species with G-alerites 
castanea, Terebratula rugulosa, Cucullcea mailleana, Columbellina 
sp., Turrilites Morrisi, and rarely Scaphites cequalis. 
Bed C contains a large derived fauna consisting of fossils in 
the state of phosphatic casts. Some of these are common in the 
beds below, and might have been derived from them; others such 
as Scaphites cequalis and Avellana cassis, are rare below but very 
common in this bed ; lastly, there are some which have not been 
found at all in the older beds. It would appear, therfore, that 
these phosphatic fossils represent the destruction and riddling 
of some bed or beds which had previously existed above B. Lastly, 
this Bed C contains a few fossils which are not phosphatised and 
belong properly to the bed ; the commonest of these is Rhynchonella 
Wiesti, a species which is closely allied to Rh. Cuvieri, and with 
it are Discoidea cylindrica, Actinocamax plenus and Ammonites 
[Douvilleiceras] euomphalus. 
The fossil evidence therefore leads us to conclude that there is 
a great gap between Beds B and C, a conclusion which is confirmed 
by the waterworn and phosphatised surface of B. But it also com¬ 
pels us to regard C as belonging to the Lower Chalk, to the very 
highest part indeed, namely, the band of Actinocamax plenus, not¬ 
withstanding the fact that there is a complete passage from it 
upward into the Middle Chalk. Physically, indeed, it forms the 
basement bed of this Middle Chalk, but we prefer to regard that 
as a local stratigraphical accident, rather than to admit the Dis¬ 
coidea and Act. plenus as Turonian fossils. 
At the extreme end of Whitland’s Cliff, above Charton Bay, the 
Beds A and B have thinned out entirely, so that C rests directly on 
a phosphatised surface of the Upper Greensand. 
4219. 
K 
