224 THE KH^TIC EOCKS OF PYLLE HILL, BEISTOL. 



exceedingly thin, but they are generally well developed in 

 the county of Somerset. They attain a thickness of from 10 

 to 15 feet in the vicinity of Bath, and in the railway cutting 

 at Weston Station, near that town, they are finely displayed, 

 as was formerly also the underlying " Gotham Marble " in 

 characteristic form. The White Lias limestones are also 

 well exposed in many quarries in the Radstock district, 

 where they are worked for road metal, and also for walling 

 and building purposes. 



The "Upper Rhastic " beds, or Rha3tic "White Lias," 

 both in the Midland counties and in the West of England, 

 are quite distinct in their lithological characters from the 

 true — or Liassic " White Lias," and contain a very different 

 group of fossils. Typically they consist of thinly laminated 

 light blue shales with bands of light grey or cream-coloured, 

 regularly- bedded or nodular, limestones, at greater or less 

 distances apart, the shales generally predominating. The 

 limestones may be, like the shales, almost entirely destitute 

 of organic remains, as they usually are in the Midlands, or 

 may contain Estherias and other fresli- or brackish-water 

 Ostraeoda, e.g., Darwinula, in vast numbers, also the remains 

 of small plants Naiadita, probably likewise of fresh-water 

 habit, and, what is most important of all, molluscan and fish 

 remains of the same species as those which are found in the 

 underlying Avicula contorta beds, and therefore character- 

 istically Rhsetic. In Somersetshire and Grloucestershire 

 the Upper Rhsetic beds are generally, but not invariably, 

 capped by that peculiar nodular limestone with dendritic 

 markings, which is known as the " Gotham Marble " or 

 " Landscape Stone," and that bed, therefore, may in this 

 district be generally taken as the upward limit of the Rha3tic 

 series.* These beds, then, from the Gotham Marble down to 

 * This is not always strictlj^ the case. For instance, in the 



