35 
LOWER LIAS. 
GENERAL DESCRIPTION. 
The Lower Lias consists in its lower portion of layers of blue 
and grey limestone, more or less argillaceous. These layers 
occur sometimes in even and sometimes in irregular bands often 
nodular and interrupted, and they alternate with blue and brown 
marls, clays, and shales ; the whole presenting, as Conybeare 
remarked, a " riband-like appearance." These beds, as a rule, rest 
conformably on the Rhaetic Beds; and where the White Lias or 
upper portion of the Rhaetic Beds is prominently developed, as in 
the south-west of England, there is usually a marked contrast in 
the colour and texture of the strata belonging to these two 
divisions. 
The higher portion of the Lower Lias consists of blue, more or 
less micaceous clays, shales, and marls, with occasional septaria, 
nodules and bands of earthy and shelly limestone, and sandy 
layers. There is no rigid plane of demarcation between them and 
the mass of limestones beneath, while the clays pass upwards into 
the lower beds of the Middle Lias, with no lithological break or 
divisional-line. The dark shaly beds are occasionally bituminous. 
The limestone-beds naturally form the higher grounds, rising 
in e3carpments, while the clays occupy low-lying tracts that merge 
into those formed by the lower beds of the Middle Lias. 
Local modifications of the Lower Lias occur on the borders of 
the Mendip Hills near Shepton Mallet, on Broadfield Down, and 
at Sutton and Southerndown in Glamorganshire, where the lime- 
stones, usually pale in colour, become granular in texture and 
more or less conglomeratic, while the clayey partings are absent 
or very meagrely represented. Peculiar siliceous varieties of the 
Lias occur near Chewton Mendip and East Harptree ; while in 
the R-adstock area the Lower Lias is much attenuated. Such 
changes are natural enough, for they are noticeable in the neigh- 
bourhood of those Palaeozoic rocks which formed land-areas durin^ 
D 
the deposition of the strata. 
The total thickness of the Lower Lias varies from about 485 
feet in Dorsetshire to about 960 feet in Gloucestershire, 465 feet 
in Northamptonshire, and about 700 feet in Lincolnshire ; but it is 
much less near Bath. 
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