138 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
This table to a large extent explains itself, but a few remarks 
on it are perhaps advisable ; thus, taking the divisions of 
Quenstedt as a starting point, it appears that the Continental 
—particularly German—geologists, take the divisions a and p 
as Lower Lias, y and 8 as Middle, and e and p as Upper, 
though some of the French geologists carry the Middle Lias 
lower down, and make it to include a good part of p. Each 
of these divisions may be justifiable in the district where it is 
adopted, but not so in others. The classification most com¬ 
monly adopted in England is that which regards all the 
zones from that of A. annulatus to A. armatus, both inclusive, 
as Middle Lias; though in the English Geological Survey 
they draw the line between the zones of A. maryaritatus and 
A. ccipricornus; and Mr. K. Tate, in a paper in the “ Journal 
of the Geological Society ” for August, 1870,* has given 
reasons for drawing the line of demarcation between the 
zones of A. obtusus and A. oxynotus. Mr. Tate’s reasons are 
entirely palaeontological, and are based on a study of the 
Gloucestershire Lias in the Cheltenham district. 
So far as Northamptonshire is concerned there seems to 
me little doubt that the divisions adopted by the Geological 
Survey are justifiable for the following reasons, which also 
hold good in most of the North Midland counties.f 
1. —There is a very marked change in the mineral 
character of the beds when the zone of Ammonites maryari- 
tatus is entered, sands, sandy shales, and ferruginous lime¬ 
stones being met with instead of clays. 
2. —The division is quite defensible on palaeontological 
grounds, for the ammonites of the group of the Capricorni 
disappear entirely and are replaced by the Amalthei group. 
3. —Very much confusion and ambiguity is saved, and the 
mapping of the district much facilitated, by drawing the line 
of demarcation between a set of sands and clay, for not only 
are they more easily distinguished in a section but the line of 
division is often sharply indicated by a line of springs ; whilst 
it is almost impossible to draw a line of boundary in the 
midst of a series of clays of almost uniform character, like 
those composing the beds below this division. 
Whether the classification adopted by the English Geo¬ 
logical Survey is best or not for general purposes it is 
certainly the best for use here, because it gives almost exactly 
* “ On the Palaeontology of the Junction Beds of the Lower and 
Middle Lias of Gloucestershire,” by Ralph Tate, Esq., Assoc. Lin. 
Soc., F.G.S., &c. 
f See “ The Geology of Rutland,” by Jno. W. Judd, F.G.S. Intro¬ 
ductory Essay. 
