150 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
more of the hard beds cutting out the usual intervening 
clay. (3) A layer of fossiliferous nodules in place of the 
continuous bed. 
The portion of the Middle Lias I am describing is often 
called the Marlstone, a term first used by Mr. William 
Smith to indicate that it contained hard stone bands. To 
this term there is some objection, for although it was applied 
to the whole of the formation between the Upper Lias and 
the zone of A. capricomus, the only part usually to be seen 
in the Midland district was the upper hard bed, here 
called the Lock bed, and so the term Maidstone got to be 
applied to this bed only. In Yorkshire Professor Phillips has 
named the equivalents of these beds the “ Ironstone ” and 
“ Maidstone” series, the Rock bed itself being called the top 
Ironstone bed, and the lower beds the Marlstone. 
Description of Beds in the “ Margaritatus” Zone. Bed “L.” 
The only account that I can find of this, the lowest bed 
of the “margaritatus” zone, and of the Middle Lias as I 
intend to speak of it, in Northamptonshire, occurs in the 
“Memoirs of the Geological Survey,” description of sheet 45 
of the maps. It was written by Mr. A. H. Green, M.A., 
F.G.S., and runs as follows:—“ At the base of the Marlstone 
hereabouts lies a bed of very hard, fine grained, dark blue 
limestone, giving out a bituminous smell when struck. It 
makes good road metal, and has been largely worked about 
Overtliorpe. It may also be seen in a brick pit north-west of 
King’s Sutton, where Twyford Lane crosses the canal.” 
There are not many sections in Northamptonshire where 
the lower beds of the Middle Lias can be seen, and for a 
considerable time I only knew of one where the lowest bed 
of the “margaritatus” zone was exposed; that was at 
Chalcomb, near to Banbury. Recently, however, we have 
been able to trace this bed over an area large enough to 
include Daventry to the north and Northampton to the 
north-east, the latter place being about twenty miles from 
Chalcomb. The bed has some decided characteristics, by 
which it can be usually identified; fossils are rather 
abundant, the matrix is peculiar, and it is a water-bearing 
bed. The particular condition of the bed at any place is 
better maintained along the line of strike than at right 
angles to it. Under Northampton it consists of a rather 
hard rock, yielding a fair amount of water ; the matrix is 
green, but there are numerous patches (inclusions) of an 
oclireous colour, quite different to the rock itself, and so 
giving to it a peculiar mottled appearance. The green part 
