ON THE CIRCULATION OF UNDERGROUND -WATERS. 411 



Marquis of Exeter, and a depth reached of 500 ft., but the Lias was not 

 penetrated, the- upper clay being above 140 ft. thick. 



Water occurs on the same horizon, in the Uppingham outlier, issuing 

 from a blue calcareous rock, forming the base of the Northampton sands, 

 at Lyddington ; springs also issue at Bisbrook. 



The upper portion of the ironstones are much peroxidized, and readily 

 pervious to water, and are called " kale " by the well-sinkers, the com- 

 pact lower portion (carbonate of iron), is the water-bearing horizon, but 

 the well-diggers consider it safer to penetrate it, and reach the Lias, "blue 

 bind," to prevent failure during droughts. 



Professor Judd states, the capacity for the absorption of rain, of the 

 Northampton sands and over-lying oolite limestone, is " practically un- 

 limited, for not only do many of the streams flowing over the boulder clay 

 instantly disappear underground, by means of swallow holes, when they 

 reach the junction of the clay and limestone or sand," but drains ai'e 

 carried into them, and artificial swallow- holes produced that never fail 

 even in the heaviest rainfalls . 



This water is given off in copious springs on the top of the lias, and 

 though containing much temporary hardness, are never chalybeate. 



The Northampton sands average twenty to thirty ft. in thickness, and 

 seldom reach more than forty, the over-lying Lincolnshire oolite at 

 Stamford is eighty ft., gradually thickening from thence northwards, and 

 thinning out entirely southwards at Harrington and Maidwell, and east- 

 wards, near Wansford tunnel. 



C. E. De Ranee. S. B. J. Skertchley. 

 Crooked drain near Norney, Ely : — 



Ft. in. 



Peat 11 



Clay (fen) 3 



Kimmeridge clay 



14 



Pit at the 70 milestone, between Littlepost and Ely : — 



Ft. in. 



Peat 1 6 



Sandy loam 1 6 



Kimmeridge clay 16 



Stone floor (septarea) , 1 3 



20 3 



C. E. De Ranee. Geological Survey. 



Great Northern Railway boring, north side of River Cam, Ches- 

 terton : — 



Ft. in. 



Made ground 4 



Black peat 2 



Gravel 10 



Kimmeridge clay 5 



21 



