ON THE CIRCULATION OF UNDERGROUND WATERS. 407 



The coal rag only appears in the Bristol area, as Longleat Park, it 

 underlies the Kimmeridge, which reaches a thickness of sixty-five feet at 

 Maiden Bradley. 



In the oolitic outcrop, ranging between Crewkerne, through Bath to 

 Wotton-under-Edge, described by Mr. H. B. W. Woodward, the coal rag, 

 when present in water bearing the Oxford clay, form the impermeable 

 layer, as does also the Cornbrash and the upper sandy beds of the Forest 

 marble, which are held up by the clayey beds beneath. 



The outcrop of the Cornbrash, between Witham Friary, South Brew- 

 ham, and Hardway to Wincanton, is marked by a line of villages, due, as 

 pointed by Professor Buckman, " not only to the fertility of the Corn- 

 brash, but to the resemblance that this porous rock, resting on the imper- 

 vious Forest marble, is a collecting ground for water, which is kept up by 

 the latter rock." 



The labours of Professor Judd, in Lincolnshire, enable the following 

 classification of the bed at the base of the oolites to be adopted : — i 



Equivalents. 



Cornbrash Cornbrash. 



Gr. Oolite clays and limestones Gr. Oolite. 



Upper Estuarian series Stoneslield slate. 



Lincolnshire oolite with Collyweston slate "] 



at its base I Inferior white. 



Northampton sands with Lower Estuarian j 



series J (Lower Freestones). 



The Lincolnshire oolites are absent in the eastern and southern por- 

 tions of the Midland district, and the Upper Extension series which 

 form the base of the great oolite series rest directly upon an eroded 

 and denuded surface of the Northampton sands, when the Lincolnshire 

 oolites are present, however, they, too, are found to be eroded, proving 

 them, like the Northampton sand, to be of inferior oolite age. 



The basement beds of the Northampton sands rest in Rutland, and 

 South Lincoln, on an eroded surface of Upper Lias clay, and generally 

 consisting of ironstone oolitic rock, forming a bold escarpment, " The 

 Cliff," stretching away for ninety miles through Lincolnshire to York- 

 shire, at the base of which copious springs arise, at the junction of 

 the lias, the beautiful Eleanor Cross at Geddington is over one. Springs 

 are thrown out in a similar situation at Pipwell, where there is the 

 remains of an old reservoir. 



At Blatherwyche Park Inlier, one well sunk to the Northampton 

 Sandrock yielded a good supply, but another was strongly impregnated 

 with sulphurated hydrogen. 



At Collyweston, a number of wells have been sunk through the thick 

 beds of the Lincolnshire oolites, into the 'red-rock,' or ironstone, which 

 itself supplies the large quantities of water used in the working of the 

 ' Slate pits.' 



To this horizon are due the springs of Wolthorpe, collected in a reser- 

 voir for the supply of Stamford. 



Very copious springs are also given off by the base of the ironstone of 

 Easton, used for the supply of that village. 



Near Stamford, a futile attempt to find coal was made by the late 



