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THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
BY BEEBY THOMPSON, F.G.S., F.C.S. 
(Continued from page 293.) 
I might give numerous instances to show that the inclina¬ 
tion of valleys, or the streams running through them, is not 
greatly different from the dip of the beds in the same direc¬ 
tion, where the streams run over clay, though in some cases 
the dip of the beds may be a little the greater and in others 
the less. The stream rising near to West Haddon runs over 
the “ unfossiliferous ” beds of the Upper Lias near to Ravens- 
tliorpe and Holdenby respectively, but over the lower portion 
of the “ Leda ovum” beds at Northampton, the distance 
being about seven miles. Again, one of the streams running 
by Kettering, and afterwards joining the Ise, runs over the 
“ Leda ovum ” beds at both Kettering and Wellingborough, 
although they are of a little lower zone at Wellingborough 
than at Kettering, distance about seven miles. 
The fall of the Nen, from its source near Staverton to 
Northampton, would give an average incline differing only a 
little from that previously deduced for the Marlstone by 
taking the height of it at Daventry and Northampton respec¬ 
tively, for the river flows frmn the Marlstone, and rapidly 
cuts down to the Lower Lias clay,* and runs over that to 
within about three miles of Northampton, and then over 
its own alluvium, though originally it ran over Middle Lias 
again ; that is, it formerly flowed over nearly the same beds 
at two places over thirteen miles apart. 
Putting together the facts just enumerated, viz.:—(1) That 
streams running over clay beds, in Northamptonshire, do not 
materially cut into them, but run over their dip plains; (2) 
that the two branches of the Nen meeting at Northampton, 
actually run over higher beds there than they do over most of 
their course, and (3) that the dip of the beds, deduced from 
such information as is available, westward of Northampton 
differs considerably from that deduced from equally reliable 
data eastward of the town, it appears evident that the dip of 
the beds is considerably reduced as we approach Northampton 
from the west, on both sides of the Nen “ fault,” though 
more on the south side than the north. I would suggest 
that the position where this change begins is approximately 
indicated by the commencement of the river alluvium, that is 
* This may at first be bed “ iVl ” of Middle Lias. (See Typical 
Section.) 
