MIDDLE CHALK—GENERAL ACCOUNT. 
365 
The Terebratulina Zone. 
This zone was established in Trance by Professor Barrois in 
1873, and identified in England by the same author in 1876. 
Since that date it has been known as tjie zone of Terebratulina 
gracilis both in England and France, but I am informed by Dr. F. 
L. Ivitchin that the true Ter. gracilis, so far as we know, is re¬ 
stricted to the higher part of the Upper Chalk, and that the form 
which is so abundant in the Middle Chalk is that named Ter, 
gracilis, var. lata, by Mr. Etheridge in 1881.* (See Fig. 59.) 
Mr. E. T. Newton agrees with Dr. Kitchin in regarding this 
form as distinct, but they consider that until the nomenclature 
of the species belonging to this genus is definitely settled it is 
best to write this form as Terebratulina gracilis var. lata, Eth, 
While therefore it is clear that we cannot continue to speak of 
the Middle Chalk zone as that of Ter. gracilis, it would be pre- 
mature to call it the zone of Ter. lata, because this may not be 
the rightful name of the species or variety. Consequently in 
this volume we shall call it simply the Terebratulina zone, using 
the name lata only where the occurrence of that form is men¬ 
tioned, but entering it in all fossil lists as Terebratulina gracilis, 
var. lata. 
This zone is the “ chalk with few flints ” of W. Phillips's section 
at Dover (1834),j* and corresponds with the Upper Marden Park 
Beds of Caleb Evans in Surrey (1870). It exhibits very uniform 
characters throughout the southern counties and as far north as 
the borders of Suffolk and Norfolk. The lower part consists of rather 
soft dull white chalk, with occasional thin seams or layers of soft grey 
marl, which is more or less argillaceous. The bedding of the chalk be¬ 
tween the layers of the marl is generally obscure, so that it comes away 
in large massive blocks. The chalk which succeeds is similar, but 
contains layers of flint nodules as well as seams of marl. In the 
South of England the flint-beds are few and far between except 
in Devonshire, where they are very numerous and caused this 
zone to be mistaken for Upper Chalk. In the counties of Cam¬ 
bridge, Suffolk, and Norfolk also they are more numerous than 
in the south, and are often elongate or finger-shaped, and curved 
or horn-shaped. In Lincolnshire and Yorkshire layers of flints are 
very frequent. 
The limits of the zone have already been discussed (p. 360), and 
we need only repeat that in this memoir it is considered to extend 
up to the base of the Chalk Eock wherever that is present. It 
is thus strictly equivalent to the Ter. gracilis zone of Professor 
Barrois, and to that so called in the Survey Memoir on the 
Neighbourhood of Cambridge (1881). 
* Geology of the Neighbourhood of Cambridge, Mem. Geol. Survey, p. 147, 
PI. 3, Fig. 14. 
t Trans. Geol. Soc., Vol. v. p. 16. 
