28 LIAS OF ENGLAND AND WALE!?: 
in their character, and that they were derived more or less 
mechanically from the waste of the older rocks that formed land- 
areas during the Liassic period. The limestones themselves are 
for the most part earthy and argillaceous, so that the materials 
constituting the mass of the Liassic strata might have been 
derived from the waste of Palaeozoic limestones and shales ; these 
old rocks being ground into calcareous mud by the breakers on 
the sea-shore or along the borders of a turbulent estuary. This 
view is indeed maintained by Messrs. Tate and Blake, who speak 
of the calcareous portions of the Lias being derived from pre- 
existing strata, and not directly from organic remains.* At the 
same time throughout the Lias the strata bear evidence of 
tranquil deposition, and only occasionally has any evidence of 
current-bedding been observed. 
It will be noted that the limestones which occur at the base 
both of the Lower and Upper Lias are locally termed Fish and 
Insect Limestones, their peculiar characters being originally made 
known by the labours of the Rev. P. B. Brodie and H. E. 
Strickland. Where definite evidence is obtained of the proximity 
of old land as in Glamorganshire and along the Mendip Hills, 
limestone? are prominently developed, sometimes to the exclusion 
of clays and shales;! ami in the Radstock area, where the beds 
are much attenuated, the higher stages of the Lower Lias, elsewhere 
mainly represented by clay, are there for the most part limestone. 
The general evidence goes to prove that the limestones, and the 
alternations of limestone and shale, were accumulated in water 
that was shallower than that of the mass of the clays.J As we 
ascend the series in the Lower Lias, the limestones become less 
and less prominent, and the upper portions of the series are 
almost entirely argillaceous Of a clayey nature also is the base 
of the Middle Lias ; but higher up there are alternations of sands 
and clays, and, at the top, the impure and sometimes highly 
ferruginous limestones known as the Marlstone. Again in the 
Upper Lias the series commences in a thin group of limestones 
and clays and passes up into a mass of clays and shales. Thus 
the conditions appear to be as follows : 
TT T - /Clays .... Deeper water. 
Upper Lias { Lin j estones and days . , 
f Marlstone - - - > Shallower water. 
Middle Lias \ Sands and clays 
I Clays 
T f Clavs 
Lower Lias { Lin j estones and clays 
-J 
> Deeper 
water. 
Shallower water. 
The occurrence of shallower-water deposits in a continuous 
series of strata may be attributed partly to changes in currents 
brought about by the shallowing of the sea-bed, owing to increase 
of sediment, and partly to the effects of denudation, whereby fresh 
rocks were brought under the influence of the erosive agents 
* Yorkshire Lias, p. '215. 
t See also De la Beche, Mem. Geol. Survey, vol. i. pp. 276-278. 
J In the Museum of Practical Geology there is a .specimen of Lower Lias lime- 
stone from Uarrow-on-Soar, that shows minute cnrrent-hedding: a feature of rare 
occurrence in that formation. 
