CHAPTER, IT. 
THE LIAS. 
GENERAL ACCOUNT OF THE STRATA. 
THE term " Lyas " was employed in a geological sense as early 
as 1719 by John Strachey, who then gave a brief account of the 
strata above the Coal-measures in Somersetshire.* Indeed, it 
has been thought that the name Lyas or (as we now spell it) 
Lias, originated as the name of the Somersetshire quarrymen for 
the argillaceous limestone-beds that form the lower part of the 
Liassic formation ;f beds that during many centuries have been 
quarried for building-stone and lime-burning. It is quite 
possible the word is a corruption of layers or liers, and it is 
noteworthy that the term " Lias " is in use by quarrymen for 
somewhat similar bands of limestone that occur in Purbeck Beds, 
Great Oolite and other formations. It has however been 
suggested that the name may be of Norman extraction, and 
derived from the French Liais.^. 
William Smith in 1799 grouped the strata as follows : 
Blue Marl = Upper (in part), Middle, and Lower Lias clays. 
Blue Lias = Lower Lias limestones. 
White Lias = Rhzetic Beds (top part). 
He took his classification from the country near Bath, where 
the Marlstone is not prominently developed, and at first some 
confusion arose in the grouping of that division with respect to 
the Upper Lias, a confusion that existed when Conybeare in 1822 
arranged the strata in the following order : 1| 
f Upper (in part), Middle, and Lower Lias 
Upper marles : v 
f Blue Lias - Lower Lias limestones. 
Stony or true has beds : | white Uas 
f Black Shales i- Rhaetic Beds. 
Lower marles -j Grey Marls J 
To John Phillips we owe our present grouping of the strata 
into Upper, Middle and Lower Lias ; divisions which he estab- 
lished in 1829 from a study of the Yorkshire Lias, and which 
have been found applicable to other portions of the country.^ 
Hence the strata have come to be grouped as follows : 
Upper Lias - Chiefly Clay. 
n/r-jji T fMarlstone and Ironstone (Rock Bed). 
Middle Lias -< ,,. , 
[_ Micaceous sands and clays. 
T . fClays. 
Lower Lias - H T i i 
{^Limestones and clays. 
* Phil. Trans., vol. xxx. p. 968. 
f De la Beche, Report on the Geology of Cornwall, &c., p. 41. 
J Applied to a hard freestone (Bret. Iduii, a stone; Gael, leac, flat stone). 
Memoirs of W. Smith, by J. Phillips, p. 1 46. 
i Conybeare and W. Phillips, Outlines of the Geology of England and Wales, 
p. 261. 
^f Geology of Yorkshire,' Part T. 
