30 
THE HALL. 
Scotch Serpentines. — Obelisk No. 155. Cubes Nos. 13 
and 165. 
Serpentine rocks occur in various localities in Scotland^, 
especially in Banffshire and Aberdeenshire, and again in the 
Shetland Isles, where they form the matrix of the chrome iron 
ore. As will be seen from the specimens, very tine varieties for 
ornamental purposes are obtained from Portsoy, on the north 
coast of Banffshire, whence this elegant material was formerly 
exported. 
Limestones. — Cubes in Wall Cases /., II., and III. Copy of 
the Farnese Hercules in Portland Stone, No. 116. 
A large number of limestones from widely different localities,, 
are here gathered together, and arranged in stratigraphical 
sequence. Most of these are derived from Jurassic rocks, since 
palaeozoic limestones are, for the most part, sufficiently indurated 
and compact to receive a polish, and may therefore be classed as 
marbles rather than as ordinary limestones ; whilst on the other 
hand, the limestones of our Upper Cretaceous and Tertiary 
formations are usually ill-fitted for building purposes. Chalk, 
however, is rather largely employed in certain districts, and 
specimens from the Middle Chalk of Beer, near Seaton, in the 
south east of Devonshire are here exhibited. Beer freestone was 
employed in Exeter Cathedral and many other edifices, and its 
use has recently been extended, chiefly for inside work. 
The Totternhoe stone , so called from a locality near Dunstable, 
is a soft sandy limestone, from the Lower Chalk, which being 
easily worked has found favour locally and is used as a building 
material in Bedfordshire and Cambridgeshire. 
The Kentish rag, of which a specimen is exhibited from the 
Iguanodon Quarry, near Maidstone, is a hard siliceous lime- 
stone from the Hythe beds of the Lower Greensand, where it 
occurs associated with a soft calcareous sandstone known locally 
as “ hassock.” The rag stone is extensively used for building 
purposes. 
From the Purbeck beds, which are mostly of freshwater for- 
mation and serve to connect the Wealden beds above with the 
Oolites below, are obtained many limestones which have long 
been worked as building stones. Several specimens are exhibited, 
mostly from Swanage in that part of Dorsetshire, known as the 
“ Isle ” of Purbeck. From the upper beds of the Purbeck group 
is obtained a compact shelly fresh- water limestone known as 
Purbeck marble, of which a polished cube is exhibited in Table- 
case II. The marble abounds in organic remains, and indeed is 
for the most part a congeries of fresh- water shells (Paludina). 
It occurs in beds which vary in thickness from six to nine inches, 
and it was much employed in this country as far back as the 
thirteenth century, especially for the slender shafts in cathedrals, 
