508 THE CRETACEOUS ROCKS OF BRITAIN. 
We now give Dr. Hume’s original notes on the analyses of 
specimens from this zone in Devonshire :—- 
“Base of Rhynchonella Cuvieri zone (eastern side 
of Beer Bay).— Inoceramus mytiloides and small Discoidea abun¬ 
dant in the rock. The residue, coarse enough for examination, 
weighed only ‘054 gramme, and of this ‘039 gramme consists 
of the silicified columnar aggregates formed inter prisma ticallv 
in Inoceramus- shells. Many of these viewed from above show 
an open hexagonal meshwork, and from the side an arrange¬ 
ment of delicate columns or films. Others, in which the change 
has proceeded further, are covered on the surface with rounded 
chalcedonic projections, the columns at the upper surface being 
expanded. In the finer residue a noticeable feature is the 
abundance of irregular or sub-hexagonal flakes of mica, show¬ 
ing very low tints from grey to almost black. These are 
mostly silvery-white Muscovite, though thin brown flakes of 
Biotite are also present. The remainder of the residue consists 
mainly of yellow glauconitic internal casts of Foraminifera , 
mostly in single spherical chambers, but not unfrequently 
also in aggregates of three or four, these combinations being not, 
however, sufficiently well preserved to determine the probable 
genus. 
“ The average size of the quartz grains is about ‘15 mm. Com¬ 
pared with the beds below, there is thus a marked diminution 
in the quantity of detrital minerals, mica and quartz being the 
only representatives. 
“ Middle Beds of Rhynchonella Cuvieri zone (Pin- 
hay Cliff, near Lyme Regis).—The amount of coarse residue in 
this sample weighed ‘027 gramme, and of this ‘017 gramme con¬ 
sisted of silicified Inoceramus fragments similar to those pre¬ 
viously described—viz., hexagonal meshes or papery films. The 
remainder consists mainly of angular quartz grains, whose 
average size was T25 mm. in diameter, and the largest does 
not exceed ‘27 mm. Glauconite grains are scattered through 
the residue, but present no special features of interest. Flakes of 
Muscovite mica are not uncommon, but no heavy minerals were 
observed. The remainder of the residue consists of the silicified 
organic fragments previously referred to. Amongst the residue 
was a beautifully preserved small idiomorphic crystal of quartz, 
the prism and rhombohedral faces being well developed. It also 
contained a few rounded gas cavities. 
‘Upper part of Rhynchonella Cuvieri Zone (Pin 
hay Cliff). The residue, in its mam features, consists of the 
remains of silicified Inocerami and foraminiferal tests, numerous 
rod-like aggregated masses of Limonite, quartz grains, the largest 
3 mm. diameter, and flakes of muscovite mica. 'Oil gramme oi 
the residue was over ‘5 mm. diameter, and consisted almost entirely 
