DOLOMITES. 
33 
its beds. The Lias extends across England, stretching in a 
north-easterly direction from near Lyme Regis, on the Dor- 
setshire coast, to Redcar on the coast of Yorkshire. The 
limestones of the Lower Lias, which are often of a blue tint, are 
usually more or less argillaceous, and form, when burnt, a 
valuable hydraulic cement ; whilst the finer stones are used 
locally as buildiug materials, and also as paving slabs : examples 
of lias limestones are shown from various localities in Dorset- 
shire, Somersetshire, and Warwickshire. The Sutton stone, from 
near Bridgend, in Glamorganshire, though at one time regarded 
as part of the “ White Lias,” or Rhaetic series, is really referable 
to the Lower Lias. 
It may be remarked that it is the practice of geologists to 
unite the Liassic with the overlying Oolitic formations under 
the general name of the Jurassic series — a name referring to the 
typical development of rocks of equivalent age in the Jura. 
Most of the Permian limestones being magnesian are described 
below, under the head of “ Dolomites ; ” whilst the majority of 
the other palaeozoic limestones have already received notice 
under the head of “ Marbles ” (p. 22 ) : a few cubes, however, 
being unpolished, find a place among the building stones. 
The Hopton Wood stone, from the Carboniferous limestone of 
Derbyshire, has been employed in the Imperial Institute ; whilst 
Devonian Limestone, from near Babbacombe and Torquay, has 
been used in the New Record Office in Chancery Lane. 
Dolomites ok Magnesian Limestones. — Cubes in Wall Case 
IV. Antinous as Bacchus, No. 59. The Giustiniani 
Minerva , No. 126. 
The Dolomites — so called because they were first examined by a 
French geologist, Dolomieu, — are essentially limestones in which 
the carbonate of lime is replaced to a greater or less extent by 
carbonate of magnesia. These magnesian limestones are largely 
developed in the Upper Permian beds of the north-east of 
England, where they often exhibit peculiar concretionary struc- 
tures, of which examples will be found in the collection of rock 
specimens in the Upper Gallery : the concretions, however, 
usually contain but little magnesia. As building materials the 
magnesian limestones are highly important, well selected varieties 
being exceedingly durable, especially when presenting a crystal- 
line texture, and containing the carbonates of lime and magnesia 
in nearly equivalent proportions. 
Dolomite is the stone which was selected, on the evidence of 
its durability at Southwell Minster, and in many other ancient 
structures, by the Commissioners for selecting the material for 
the Houses of Parliament. It is also the stone employed in the 
construction of this Museum. Experience has shown, however, 
that although some varieties are highly satisfactory, others are 
not well adapted for exposure to the atmosphere of London. 
