RH.ETIC BEDS. 243 



The Rhaetic Beds, where fully developed, consist of the follow- 

 ing divisions : — 



3. White Lias, from I to 25 feet. 

 2. Black Shales, ,, 8 to 30 ,, 

 I. Grey Marls, ,, 10 to 50 ,, 



The total thickness of the series is sometimes as much as 150 feet. 

 W/ii'/e Lias. — The name White Lias is a quarryman's term, 

 which was adopted by William Smith (1815), the stone being, as 

 a rule, very distinct from the Blue (Lower) Lias above it. The 

 White Lias comprises beds of white, pale-grey, and cream- 

 coloured limestones and marls, which maintain much uniformity in 

 tint and texture. The top-bed in the neighbourhood of Bath and 

 Radstock is a hard, compact and smooth-grained stone, known as 

 the Sun Bed ; the term Jew Stone is sometimes applied to this bed 

 (which may consist of two or more layers), near Wedmore and 

 Street, and other parts of Somersetshire, south of the Mendip Hills. 



Fig. 38. — Section West of Weston Railway Station, near Bath. 





r< — ^ 







Lower Lias. Valley Gravel and Rubble. 



White Lias (Rhaetic). Lower Lias. 



The Cotham or Landscape Marble, so well known from the 

 dendritic markings which occur throughout it, is found at or near 

 the base of the White Lias. It is a hard, compact limestone, like 

 the Sun Bed, with generally an irregular mammillated or corrugated 

 surface, and it is found in impersistent masses from two to eight 

 inches thick. The name Cotham Marble is derived from Cotham 

 House, north of Bristol.^ This stone is generally present in the 

 southern part of Gloucestershire and Somersetshire, extending 

 even to the coast-section between Axmouth in Devonshire and 

 Lyme Regis in Dorsetshire. Between Bath and the Mendip Hills, 

 the Cotham Marble is frequently turned up in the ploughed fields, 



^ E. Owen, Observations on the Earths, etc., for some miles about Bristol, 1754. 



