1870.] _ SHARP—NORTHAMPTONSHIRE OOLITES. 375 
to the total thickness of D and E, the sequence of the beds of the 
wells-section being also favourable to such an assumption. 
It is noticeable, however, that at the “ Old” Duston pit the green 
colouring of the beds begins with the Astarte zone, while in this 
Ironstone section it is only observable lower down. The absence of 
the green colouring in the higher beds of both sections is probably 
due to oxidation, the effect of atmospheric influence. In the “ old” 
pit, a very thick mass of rock is superimposed upon the Astarte zone ; 
and consequently such atmospheric influence has not permeated that 
and lower beds; but in the Ironstone quarry the Astarte zone lies 
comparatively near to the surface, and considerably above the level to 
which that influence has penetrated. This difference in circumstances 
of position will probably account for the apparent discrepancy in 
the range of the green colouring of the beds in different sections. 
The parallelism of these beds with the lower beds of Bass’s 
pit (/) is not only suggested by position, but is confirmed by the 
fact of the identity of some characteristic fossils found in both 
sections, notwithstanding the absence from the last-named pit of 
the Astarte zone: for instance, in the lower beds of Bass’s pit are 
found two large species of Plewrotomaria (armata? and a species 
near to Marcousana of D’Orbigny); and the same forms (unmis- 
takably identical with those from Bass’s pit) occur in the Duston 
Ironstone beds. The lowest bed, also, like that in the last-named 
pit and in the Kingsthorpe pit, is full of rounded pebbles or con- 
ceretionary nodules. 
That these beds are not higher up than the Inferior Oolite is 
abundantly shown by the fossils exhibited; while the view that 
these beds are possibly equivalent to Dr. Wright’s Frocester 
Cephalopoda beds is strengthened by the occurrence of Ammonites 
jurensis (?), and in three other pits of Rhynchonella cynocephala ; 
and that they have a transitional character, by the probable presence 
of Pholadomya ambiqua, Ammonites bifrons, A. opalinus, and some 
other fossils which would tend to such a conclusion. 
It cannot be conceived that there could have been a point in time 
at which the period of the Upper Lias definitely ceased and the 
period of the Inferior Oolite as definitely commenced. One must 
have merged into the other, and life-forms have been gradually 
transmuted into or superseded by other life-forms, during a con- 
necting period of longer or shorter duration; and my suggestion is, 
that we have in the lower beds of the Northampton Sand a strati- 
graphical representative of a portion of such transitional interval *. 
Before leaving this remarkable section, I may be excused if I 
offer a few words upon the ferruginous character of these beds. I 
need not say that they are not in their original condition. The 
numerous living organisms of which these fossils (many of them, as 
it were, cast in iron) are the enduring monuments, could not pos- 
sibly have existed in waters charged with iron to the degree appa- 
rently indicated by the present condition of the rock. The iron 
must have been introduced after the deposition of the sedimentary 
* See Dr. Lycett’s opinion in note to the Blisworth Area. 
