185 
CHAPTER VII. 
MIDDLE LIAS. 
GENERAL DESCRIPTION. 
THE Middle Lias consists in its lower portion of bluish-grey 
micaceous marls and clays, passing upwards into laminated sands 
and clays with nodular layers of limestone and calcareous sand- 
stone. These beds, in places, are surmounted by yellow micaceous 
sands, with indurated masses or " doggers " of calcareous sand- 
stone. The higher portion of the Middle Lias comprises variable 
layers of stone, to which the name of "Rock Bed" is sometimes 
applied, but the beds are more usually grouped under the general 
name of Marlstone. 
The term Marlstone was at first employed by William Smith 
(1815-16), to include not only the Middle Lias "Reck Bed," but 
the basement limestones of the Upper Lias, argillaceous limestones 
for which the name Marlstone was especially appropriate. The 
term now is restricted to the Middle Lias, and is sometimes 
employed, as Marlstone Series, to embrace the entire formation. 
The Marlstone proper, or upper portion of the Middle Lias, 
includes, in places, beds of yellow micaceous sand and sandstone 
(before noted), but its moat characteristic strata are beds of tough 
iron-shot and earthy limestone that occasionally contain small 
calcareous nodules. These beds, where unweathered, are blue or 
greenish-grey in colour, but near the surface they become brown, 
and being extensively quarried they are then known as the " Brown 
Rock." These earthy limestones pass on the one hand into 
calcareous sandstones, and on the other into valuable beds of 
ironstone. The iron-shot grains that occur in some of the beds, 
are tiny spheroidal grains of peroxide of iron, that sometimes 
exhibit oolitic structure ; but as noted in reference to beds in the 
Lower Lias, an iron-shot appearance may be independent of true 
oolitic concretions. 
The Middle Lias is thus on the whole more variable in character 
than either the Lower or Upper Lias. 
The beds of sand that occur above the clays in Dorsetshire and 
Somersetshire, assist in forming an escarpment in these southern 
counties, but the sandy beds are less defined in Gloucestershire 
and Oxfordshire, and are nowhere very prominently exhibited in 
the country northwards to Lincolnshire. In Yorkshire the lower 
part of the Middle Lias has been called the " Sandy Series," and 
the upper part the " Ironstone Series " ; so that the general 
characters of the subdivisions are there maintained. 
The Rock Bed, which is but feebly represented on the Dorset- 
shire coast, is nowhere well developed in the area near Beaminster. 
Further north it attains eorne importance at Ilminster and South 
Petherton, but eastwards, near Yeovil and South Cadbury, it it 
