94 



THE LIAS AMMONITES. 



The " Marlstone " of English Geologists forms a marked division of the Middle Lias. 

 In the Midland Counties it consists of a lower portion, composed of yellowish-brown 

 sandy beds, with thin bands of limestone and ferruginous nodules, and of an upper 

 portion or rock-bed, formed of impure limestone containing many fossil shells in good 

 preservation ; it weathers brown externally from the oxidation of the iron it contains, 

 whilst it is blue internally when broken with the hammer. This rock-bed forms a solid 

 capping to the lower arenaceous beds, the more rapid erosion of which along their out- 

 crop in Marlstone districts produces those terraces and tabulated promontories, as at 

 Gretton, Alderton, Durableton, Churchdown, and Stinchcombe Hills, which impart such 

 a picturesque effect to the physiographic features of the western escarpment of the Cottes- 

 wolds ; whilst the steep slopes descending from the edges of the platforms to the Lower 

 Lias plain below are composed of softer beds of Liassic sands and clay that have under- 

 gone a greater amount of atmospheric erosion. 



North of Cheltenham the Marlstone is exposed in large quarries at Bredon, Alderton, 

 Dumbleton, and Gretton Hills, where it was formerly worked for road-material. From 

 Gretton I collected a large number of fossil shells, many of which had their tests in 

 good preservation. In these localities, however, it is difficult to separate the Margaritatus- 

 from the Spinatus-htdi. South of Cheltenham the Marlstone is found at the summit of 

 Churchdown Hill, a remarkable circumdenuded outlier of the Cotteswolds, and on the 

 western slope of Robin's Wood Hill, another outlier of the same ; at Frocester Hill it forms 

 a terrace of hard calcareo-siliceous limestone, which rests upon brown and greyish sands, 

 containing bands and nodules of ferruginous ironstone ; the whole of the Middle Lias 

 here measuring about 150 feet in thickness, and divisible into Jamesoni^ Ibex, Henleyi, 

 and Margaritatus beds very similar in their petrological characters to those already 

 described. The fine mass of Stinchcombe Hill, which projects like a bold headland into 

 the valley, exhibits a greater thickness of Marlstone than any other section in the Cottes- 

 wolds ; the Newent quarry near the village of Stinchcombe has twenty feet of Marlstone, 

 covered by five feet of Upper Lias clay. At Wotton-under-Edge the Middle Lias is 

 186 feet thick, as measured by my old esteemed friend Professor A. Ramsay, F.R.S., 

 Director- General of the Geological Survey, who many years ago surveyed this district, 

 and was kind enough to draw for me the following profile of this interesting bit of the 

 Cotteswold range. 



Turnpike Koad. 

 I 



Diagram showing the Strata between Syraond's Hall Hill and Wotton-under-Edge (' Jouru. Geol. 



Soc.,' vol. xvi, p. 307. 



This section shows the succession of Jurassic strata from Symond's Hall HiU to the 

 Vale of Gloucester, and which, read in ascending order, includes — 



