UPPEK LIAS: NORTHAMPTON. 273 
In the Upper Leda-ovum clays, the fossils occur mostly in clusters in hard 
nodules, and among them Mr. Thompson records the following ; 
Saurians. 1 Astarte minima. 
Ammonites bifrons. 
cornucopia. 
elegans. 
heterophyllus. 
Lilli (near to A. comensisX ). 
X lympharum. 
Belemnites (several species). 
Dentalium (gracile) elongatum. 
liassicum. 
Euomphalus (?) minutus. 
Area elegans. 
X Cardium (Protocardmm) substriatulum. 
X Gresslya abducta. 
Inoceramus dubius. 
Modiola gregaria (cuneata?). 
X Avicula substriata. 
Ostrea sandalina. 
Pecten demissus. 
Trigonia northamptonensis (near to T. 
literata X ). 
X Discina reflexa. 
Lingula Beani (not found in lower beds] 
The species marked X are recorded by Messrs. Tate and Blake from the 
zone of Ammonites jurensis,* and Mr. Thompson is of opinion that this zone 
may to a certain extent be represented in Northamptonshire, by these Upper 
Leda-ovum clays. 
The total thickness of the Leda-beds in Mr. Thompson's opinion cannot be 
less than 50 feet ; but estimates are necessarily rather doubtful, as the sub- 
divisions of the Leda-ovum Beds " merge gradually one into the other." 
A number of Foraminifera from the Leda-ovum Beds, have 
been described by Messrs. W. D. Crick and C. D. Sherborn.t 
As Mr. Thompson remarks, in Northamptonshire there is no 
difficulty in deciding the stratigraphical boundary between the 
Upper Lias and Inferior Oolite, for the junction between the two 
formations is, as a rule, sharply defined, and sometimes presents 
evidence of an unconformity. The Basement-beds of the Inferior 
Oolite (Northampton Sands) here belong mainly to the zone of 
Ammonites opalinus, but they contain, not uncommonly, specimens 
of A. jurensis, wherefore the zone of A. jurensis is to some 
extent represented in the Northampton Sands.J 
The fact that the junction is often very sharply defined, and 
that there is evidence of local erosion would suggest that portions 
of the zone of A. jurensis were in places unrepresented, and this 
appears to be the case. On the other hand "at one or two places^ 
there is evidence of a passage from the Upper Lias to the 
Inferior Oolite, with, apparently, only a slight cessation of 
deposit." I have seen instances of this gradation. 
Comparing the Basement-beds of the Inferior Oolite (Northamp- 
ton Sands) with the Dogger of Yorkshire, there is evidence of 
much agreement in general structure and fossil contents ; but 
there is no evidence at present of the occurrence in Northampton- 
shire at this horizon, of Ammonites striatulas and other Ammonites 
that characterize the underlying shales in Yorkshire. The absence 
of these Ammonites cannot alone be taken as proof of any 
break in the sequence, but the stratigraphical and palaeontological 
* Yorkshire Lias, p. 190; see also Fox- Strangways, Jurassic Bocks of Yorkshire, 
vol. i. p. 136. 
f Journ. Northamptonsh. Nat. Hist. Soc., vol. vii. p. 67. 
J Thompson, Journ. Northampton Nat. Hist. Soc., vol. v. p. 75 ; E. T. Newton, 
Gcol. Mag., 1891, p. 493. See also S. S. Buckman, Journ. Northampton Nat. Hist. 
Soc., vol. vi. p. 7. ; Mr. Buckmaa regards the form fouud in the zoue of A. opalinus 
as deserving a distinct Tiainc, and lie has called it Ammonites (Lyto:eras) Wrighti, 
E 70859. 
