890 STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
and an upper marked by Pecten asper. These strata are well developed 
in Devonshire and Somerset. There the ‘‘ Blackdown beds” below, 
linked with the Gault, contain a numerous fauna, including Ammonites 
Goodhalli, Hamites alternatus, Cytherea parva, Venus submersa, Arca glabra, — 
Trigonia aleformis, Pecten laminosus, Janira quinquecostata, J. quadricostata, 
J. equicostata, Ostrea (Exogyra) conica, Vermicularia polygonalis ; while the 
‘‘ Warminster beds” above correspond to the “ zone of Holaster nodulosus ” 
of M. Hébert, and the “ zone of Pecten asper” of Dr. Barrois, and con- 
tain Ammonites varians, A. Mantelli, A. Coupet, Belemnites ultimus, Pecten 
asper, Ostrea frons (carinata), Terebratella pectita, Terebratula biplicata, 
T. squamosa, Rhynchonella compressa, R. latissima, Pseudodiadema Michelin, 
Peltastes clathratus, Discoidea subucula, &c. A tolerably abundant series 
of corals has been obtained from the Devonshire Upper Greensand, n 
fewer than 21 species having been described.’ 
The so-called Greensand of Cambridge (p. 809), a thin glauconitic 
marl, with phosphatic nodules and numerous (possibly ice-borne) erratics, 
was formerly classed with the Upper Greensand, but has recently been 
shown to be the equivalent of the Chloritic marl, forming really the 
base of the Chalk marl and lying unconformably upon the Gault, from 
the denudation of which its rolled fossils have been derived? Further 
north, at Hunstanton, in Norfolk, the same horizon may be represented 
by the “Red chalk”—a ferruginous, hard, nodular chalk zone (four 
feet) at the base of the chalk and resting on the Upper Neocomian 
‘“‘ Car-stone,” the Gault being absent. 
Chloritic Marl.—This name has been applied to a local white or light 
yellow chalky marl lying below the true Chalk, and marked by the 
occurrence of grains of glauconite (not chlorite) and phosphatic nodules. 
It varies up to 15 feet in thickness. Among its fossils are Ammonites 
laticlavius, A. Coupei, A. Mantelli, A. varians, Nautilus levigatus, Turrilites 
tuberculatus, Solarium ornatum, Plicatula inflata, Terebratula biplicata. It 
forms the base of the ‘‘ Holaster subglobosus group,” or assise. 
Chalk Marl is the name given to an argillaceous chalk forming with the 
chloritic marl, where the latter is present, the base of the true Chalk 
formation. This subdivision is well exposed on the Folkestone cliffs, 
also westward in the Isle of Wight, where a thickness of upwards of 
100 feet has been assigned to it. Among its characteristic fossils are 
Plocoscyphia mzandrina, Holaster levis (var. nodulosus), Rhynchonella 
Martini, Inoceramus striatus, Lima globosa, Plicatula inflata, Ammonites 
cenomanensis, A. falcatus, A. Mantelli, A. navicularis, A. varians, Scaphites 
wqualis, Turrilites costatus, 
Grey Chalk.—The lower part of the Chalk has generally a somewhat 
greyish tint, often mottled and striped. The subdivision comprising 
the paleontological zones of Holaster subglobosus and Belemnites plenus 
attains its fullest development along the shore-cliffs of Kent, where it 
attains a thickness of about 200 feet. According to Mr. F. G. H. Price,® 
it is there divisible into five beds. Of these the lowest, eight feet thick 
= lower part of the Ammonites varians zone), contains among other fos- 
sils Discoidea subucula, Pecten Beaveri, Ammonites varians ; the second bed 
(11 feet) contains many fossils, including Ammonites rhotomagensis, A. Man- 
1 P. Martin Duncan, Q. J. Geol. Soe, xxxv. p. 90. 
* Jukes-Browne, Q. J. Geol. Soc, Xxxi, p. 272, xxxiii. p. 485 ; “ Geology of Cambridge,” 
Mem. Geol. Surv. 1881. 4 Q. J. Geol, Soc. xxiii. p. 436, 
