150 THE BATH OOLITE PERIOD. CHAP. 



and on the other, with the sandy and calcareous deposits lying 

 above the iron ores which rest on the lias of Oxfordshire. Whether 

 they are continued, or in what way represented in Northamptonshire 

 and Lincolnshire, may be considered at the end of this chapter. 



MIDDLE DIVISION or THE GREAT OOLITE. 



By those who live under the shadow of Combe Down and the other 

 hills near Bath, the title of Great oolite will be readily conceded 

 to the thick rock which crowns those elevations with a wreath 

 of valuable freestone. From quarries in this rock Bath and many 

 towns and cities have been built ; and it preserves its importance 

 and superiority, as compared with the other members of the system, 

 till, as we go northward, we reach the vicinity of Gloucester and 

 Stroud. Here, as already stated, the thick rocks of Painswick and 

 Leckhampton, which belong to the Inferior oolite, become the most 

 prolific centres of valuable freestone. The Great oolite, however, 

 continues to be a considerable member of the series, as we proceed 

 by Thames-head and Cirencester, Northleach and Burford, Shipton 

 and Chadlington, Stonesfield and Enslow Bridge. Along both sides 

 of the Cherwell it maintains a considerable thickness, stretching 

 to the northward, toward Deddington and Aynhoe, and turns off 

 by Brackley and Buckingham to Blisworth and Northampton. 

 After leaving the downs over Bath, we find the thickness of the 

 Great oolite to diminish northwards. From 105 feet, near Bath, 

 it sinks to 60 in Gloucestershire and Oxfordshire, and to 30 feet in 

 Northamptonshire. These measures are independent of the variable 

 series above, known as Forest marble and Bradford clay. 



The composition and structure of the rock are inconstant ; 

 when purely oolitic, with few or no shells, it is usually massive 

 and good freestone. When shells become plentiful and range 

 themselves in layers (sometimes oblique), the stone becomes more 

 fit for rough walling and strong foundations than house-build- 

 ing. This kind of 'ragstone' is like forest marble, and often is 

 not easily distinguished from that rock. In Oxfordshire usually 

 the beds of stone are more or less separated, especially in the upper 

 parts, by thinner bands of marly clay, which appear to have been 

 derived from the same source and to indicate operations of the 

 same kind as the clays of the forest marble above. Those clays 



