162 CELESTINE DEPOSITS OF THE BRISTOL DISTRICT. 
blue colour the mineral sometimes possesses. Analyses show 
that celestine contains a very high percentage of sulphate of 
strontium, the amount varying from 83-99 per cent., the 
average being about 94 per cent. 
Celestine is specially well seen in the Bristol District, occur- 
ring as thin beds and irregular deposits in the Triassic marls, 
especially near the boundary between the Ked Marls and the 
Tea Green Marls It is worked for commercial purposes at 
many places, especially in the Yate and Wickwar district. 
Starting from the Golden Valley, near Bitton, the exposures 
have been followed through Wapley, Yate, and Sodbury, near 
the south end of the Wickwar tunnel, and Cowshp to Ash- 
worthy. The mineral occurs also near Charfield, to the north 
of the Carboniferous limestone ridge which forms the edge of 
the Bristol coalfield. 
To the south of Bristol it is found on the north side of the 
Mendips near Winford, and at Regilberry, and on the south 
side of the Mendips at Easton between Cheddar and Wells. 
In all these places the celestine is found in pockets. Often 
the deposit will run across several fields, but not continuously, 
as there may be several breaks, and while from one excavation 
several thousand tons may be obtained, the next may yield 
only a small quantity. Some of the excavations show two 
or more beds at different depths, separated by marl and some- 
times introduced between the beds of the underlying Palaeozoic 
series. Generally near the surface will be found isolated 
celestine masses, then may come an irregular bed of the mineral, 
this may be followed by a deposit of marl and lower again 
another bed of celestine. The beds are not continuous, but 
sometimes thin out, or break off suddenly, but commence 
again further on at the same level. The deposits vary in 
character. In some the celestine forms a mixture of angular 
and subangular masses of irregular shape and varying size ; 
in other cases the fragments are rounded. There occur also 
large geodal masses sometimes weighing several hundred- 
