TIIE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
99 
beds now than formerly owing to excessive, and in some cases 
indiscriminate agricultural drainage. No doubt both of these 
causes have been in operation in Northamptonshire, but the 
former has had much more effect than the latter. 
I tried to form an estimate of the amount of water that 
might reasonably be expected to get into the Middle Lias of 
the county annually, supposing no artificial impediments were 
interposed, and so to see what relation it bore to the amount 
actually extracted from the Maidstone wells at Northampton. 
Almost at the outset it became evident that any such estimate 
founded upon catchment area would be of little or no value, 
but the attempt considerably modified my ideas of the extent 
of catchment area in the direction of reducing it. On looking 
at a geological map of the district, it will be noticed that 
nowhere does the Middle Lias cover a very extensive uninter¬ 
rupted surface area, owing to numerous Upper Lias hills rising- 
above it, or to valleys cut through it, a natural consequence 
of its comparatively small thickness. Besides this, even where 
coloured as Marlstone in the maps, it is not unfrequently 
covered b}’’ the lowest beds of the Upper Lias* and these by 
interposing one or more thin clay beds between the surface 
and the Bock-bed would materially reduce the intake of water, 
as would also the capping of boulder clay that is sometimes 
found similarly situated. The Middle Lias is still more often 
covered with drift in the form of thick beds of sand or gravel; 
indeed, so completely is the Middle Lias catchment area 
covered to the North-west of Northampton that the boundaries 
of its outcrop are only approximately indicated on the maps 
by dotted lines. This drift can scarcely be regarded as 
injurious, and may be very helpful, by, as it were, extending 
the catchment area of the Middle Lias. 
The effect of streams in reducing the water-bearing capacity 
of the Middle Lias of Northamptonshire is no doubt greater 
than that of all of the other causes named, for not only do 
they destroy the continuity of the bed by cutting it up into 
outliers and peninsula-like masses of no great storage capacity, 
but they very considerably drain these and the escarpments of 
the main bed. Also the main mass of Middle Lias to the 
South-west of Northampton is well drained by streams. 
The Nen, Cherwell, Learn, and Avon each receive consider¬ 
able contributions from the Middle Lias. 
* I have so frequently found fossils from the stone beds at the base 
of the Upper Lias in Northamptonshire, marked as Marlstone, that I 
think they must at one time have been regarded as Middle Lias. 
