14 



INFERIOR OOLITE. 



Rising from beneath the central members of the system, the Inferior Oolite and 

 Lias appear in great force along the escarpments of the Cotteswold Hills. As the beds 

 of these two formations have a general inclination to the east and south-east, at angles 

 varying from 5° to 12°, it is evident that, in crossing from the Cotteswold Hills to the 

 Severn, the strata of each group will be seen to emerge from beneath those which have 

 been deposited over them. In this way we make our first transverse section. 



The following description applies, therefore, to such strata as are found in " de- 

 scending order," upon any straight line drawn from the escarpment of the Cotteswolds 

 to the banks of the Severn. See coloured section PL 29. fig. 1. and this wood-cut. 



(West.) 



(East.) 1. 



New Red r h. Red and green Marl. 



1 rfi 



Sandstone. Xi. Sandstone and Marl. 



Lias.- 



-d. Upper Lias. 

 e. Marlstone. 



/. Lower Lias Shale. ^ c 



.ff. Limestone of the Lower Lias Shale. 



T „ . fa. " Gryphite Grits." 

 Interior 



Oolite 1 Cheltenham Bnilding-ston< 

 01 6 * I - "Pea Grit." 



Inferior Oolite. 



The rocks composing this formation in the Cotteswold Hills are all more or less 

 calcareous. They rise to the west, from beneath certain clays and flaglike beds 

 (Stonesfield Slate) , and occupying a thickness of about. 1 50 feet, are divisible into three 

 parts. 



(«. of section.) The uppermost is a brown calcareous grit, of a very coarse aspect, owing to the 

 number of shells it contains, among which Gryphcea Cymbium, Lima proboscidea, Trigonia 

 costata, and Pholadomya ambigua are the most abundant. This "Gryphite grit" caps the hills, and 

 is extracted for the use of the roads 1 . 



(b. of section.) The central division is much the thickest, and may be subdivided into three parts. 



1st. Upper Ragstone, and thin-bedded Oolite. 



2nd. A fine-grained, light-coloured Oolite, the Cheltenham building-stone, which varies from 

 thirty to forty feet in thickness, and when quarried under ground is dressed with facility 2 . It is 



1 I named this stratum "Gryphite grit," from the prevalence of the " Gryphcea Cymbium." This name 

 and that of Pea grit (p. 12) are local terms, applicable only to the structure of the Upper and Lower strata of 

 the Inferior Oolite of Gloucestershire. (See Sketch of the Geology ot Cheltenham, 1834. J. Murray.) 



2 In general, the Oolitic freestones, from whatever part of the system they are derived, on being exposed to 

 the atmosphere, lose much of that moisture which they naturally possess under ground, and become much 

 harder. The quarries of Ketton, in Northamptonshire, which are in the Great Oolite, yield, like those of Chel- 

 tenham, blocks of very large dimensions. These blocks are easily cut with the saw on being first extracted, 

 but become rapidly harder on exposure to the atmosphere, and when struck with a hammer clink like a piece 

 of metal. 



