398 Dr. A. Morley Davies—Zones of the 
(vertumnus, gregarium, vernon) I am unable to say, nor can I venture 
ut present a correlation with the late M. Robert Douvillé’s sequence 
at Dives.’ 
The. higher pre-cordatum zone (perhaps answering to Mr. Buckman’s 
scarburgense zone) has been exposed in a well-sinking near Studley? 
and in the Great Western railway cutting immediately north of 
the tunnel in Rushbeds Wood, Brill. In both these cases the 
ammonites recorded as C. cordatum were finely ribbed forms of the 
tenurcostatum type. 
8. The cordatum or vertebrale zone.—The zone in which the true 
Cardioceras. cordatum (J. Sowerby) occurs is only represented in the 
district under immediate notice by the Arngrove Stone or Rhazella- 
chert, but westwards it is well represented by part of the Lower 
Caleareous Grit. The bcarmatum zone which follows it in the 
Abingdon district is not found at all to the east. 
9. The martelli zone (plicatilis zone, auctt.).—This is the Upper 
Corallian of the areas where the coral facies is developed. Apart 
from its characteristic perisphinctid ammonites, it 1s recognized by 
the abundance of Hxogyra nana (J. Sowerby) * in its lowest beds. 
The calcareous facies of these beds is seen as far east as Wheatley, 
beyond which there is a sudden change into Ampthill Clay. The 
basement beds characterized by great numbers of /. nana were 
observed and mapped long ago by Polwhele, and recently by H. B. 
Woodward, but the finest exposures of them were obtained still later 
in the railway cuttings at Ashendon junction and Dorton. Here they 
consisted of varying beds—bluish clay, white limestone, and marly 
beds full of brown oolite-grains. Some of the latter closely resembled 
the Elsworth rock except that they were unconsolidated; others, 
by the abundance of oysters and serpule, approached in character 
the Gamlingay basement bed. Plentiful radioles of Cidaris smithi, 
Wright, with a few of C. florigemma, Phillips, inked them with the 
caleareous beds to the west. They were overlain by over 30 feet of 
drab clay with beds of soft argillaceous limestone, the clay yielding 
oysters of the deltoidea and discordea types, the stone-beds Perisphinctes 
chloroélithicus, Giimbel, and other maréelli-zone fossils. In short 
these railway cuttings link up Polwhele’s clay in the most satisfactory 
manner with the typical Ampthill Clay and its basement beds, including 
the Elsworth Rock. 
‘Neither Seeley nor Roberts, to whom we are indebted for most of 
our knowledge of the Ampthill Clay, seems to have questioned its 
equivalence to the whole of the Corallian. Mr. C. B. Wedd, by his 
discovery of Elsworth Rock as a base to the Coralline Oolite of 
Upware, made it highly probable that the Ampthill Clay is Upper 
Corallian only. H.B. Woodward was cautious in his correlation. 
He wrote of the abrupt termination of the Corallian stone-beds at 
1 Cardiocératidés de Dives (Mém. Soc. Géol. France), 1913. 
2 Davies, Q.J.G.S., lxiii, p. 40, 1907. 
3 Davies, Proc. Geol. Assoc., xx, p. 185. 
4 The holotype of H. nana came from the Lower Kimmeridge Clay of 
Shotover. Should the much commoner Corallian form prove distinct from 
this, it would probably take the name Haogyra mima (J. Phillips). 
*° C. B. Wedd, Q.J.G.S., liv, pp. 614-16. 
