24 
THE HALL. 
The shell-marbles usually contain the remains of Brachiopoda , 
organisms which are so called from having two long ciliated 
“ arms ” ( brachion Gr., an arm ; pons, a foot). These are “ shell 
fish,” furnished with two valves which are never quite equal, 
but since each valve is equal-sided the forms are symmetrical. 
In these points they differ from the ordinary bivalves, or true 
molluscs, which are mostly equivalved but rarely quite equilateral. 
From the resemblance of certain brachiopod shells to antique 
lamps, they are commonly called “ lamp shells ; ” the hole corre- 
sponding to that which in a lamp admits the wick, serves in the 
lamp shell for the passage of the pedicle by which the animal 
attaches itself to submarine objects. Spirifera and Productus, 
two genera of the above class, are the most abundant in these 
limestones. 
The black marble is a bituminous limestone, found especially in 
descending into Monsal Dale from Little Longsdon. Machinery 
for cutting and polishing this marble was first used at Ashford 
in the year 1748, and marble works are still in operation in 
this locality. 
In this collection the following localities of Derbyshire 
marbles are represented, viz., — Wirksworth, Middleton, Bonsall, 
Matlock, Nether Haddon, Allport, Monyash, Oneash, Sheldon, 
Ashford, Flagg, Stony Middleton, Buxton, Miller’s Dale, Ricklow 
Dale, and Tideswell. 
A cube of crinoidal marble, extremely similar to some of the 
Derbyshire marble, from the Yoredale rocks (Lower Carboni- 
ferous) of Dent, in the west of Yorkshire, is placed with the 
specimens from Derbyshire in Case I. As Dent was the birth- 
place of Professor Sedgwick a pedestal of this marble has 
been selected as an appropriate support to the bust of this 
distinguished geologist. (No. 203.) 
Staffordshire Marbles. — Columns, <$cc., Nos. 129 and 186. 
Tazza 64. Inlaid worlc, 145 and 161. Cubes in Case II. 
The marbles in Staffordshire present but little variation from 
those of Derbyshire, the adjoining county. Their geological 
positions are the same, and they present similar general 
characters. Specimen's of Staffordshire marbles are exhibited 
from Wetton and from Ecton. 
The variety of coloured marbles which the two counties of 
Derbyshire and Staffordshire produce has led to the manufacture 
of mosaic work of a very beautiful description. Indeed, some 
of the inlaid tables, tazze, and other marble ornaments, may not 
unworthily be compared with the far-famed Florentine mosaic 
work. In addition to the inlaid tables in this Hall, there will 
be found some interesting specimens of this kind of work in 
the horse-shoe case on the principal floor. 
