520 Notices of Memoirs—Sandstones of the Bristol Coal-field. 
Cambrian group, as in the Pebidian rocks at St. Davids, and 
elsewhere. ‘There are also some other exposures of the Pre-Cambrian 
rocks in the adjoining areas, and one very interesting section was 
carefully examined by Prof. Hughes and myself, to the east of the 
Trawsfynnydd road, between Caean Cochion and Penmaen, where 
the Cambrian conglomerates could be seen resting unconformably 
upon the older series, and large masses of the latter found plenti- 
fully in the conglomerates. 
VIIL—Own tur Sanpstones AND Grits oF THE Lower AND Mripp1Le 
Series OF THE BristoL CoAL-FIELD. 
By Epwarp WerueErep, F.G.S. 
IT\HE Bristol Coal-field is noted for its series of grits and sandstones, 
and these probably have their equivalents, in the South Wales 
and Forest of Dean Coal-fields, as well as in that of Somersetshire. 
They serve as stratigraphical landmarks ; and it was the object of 
the paper (1) to compare the grits of the above Coal-field with one 
another, with a view of ascertaining whether there were distinguish- 
ing features which might enable them to be respectively determined, 
and assist in correlation. (2) To examine the chemical and physical 
conditions. (3) To note changes which occur when rocks are in 
contact with carbonaceous matter. The first point raised was the 
application of the term grit and sandstone. The author confirmed 
the statement of Mr. Sorby, in his presidential address to the Geo- 
logical Society in 1880, to the effect that the Carboniferous Sand- 
stones were composed of angular grains. Of those examined by the 
author, the grains of the Millstone Grit were the least angular. It 
was also pointed out, that as rocks show such variation of coarseness 
in the same deposit, this could not be taken into consideration as a 
test for grit. It was therefore suggested that the term grit should 
be confined to those rocks which show angularity of grains, irrespec- 
tive of coarseness; and the term sandstone to those which are com- 
posed of rounded grains (i.e. from which the angularity has been 
removed). In any case, the term grit must be more generally ap- 
plied to Carboniferous rocks than has been the case hitherto. 
Reference was then made to ‘duns,’ which was defined as those 
Carboniferous beds intermediate between grit or sandstone and clay. 
In mining operations, where the ‘driving’ of branches was by con- 
tract, questions arose between employer and employed, in the case 
of § hard duns,’ as to whether it is ‘stone’ or ‘duns,’ double price 
being paid for driving in the former. It was also important for 
geological purposes, in the construction of sections, that there should 
be an easy and ready test for this determination. The author sug- 
gested that the scratching of glass would be a suitable one, which 
would represent a hardness of 7 for rock which scratches glass. 
The chief deposits of rock in the Coal-field were then referred to, 
in ascending order, commencing with the Millstone Grit. Several 
samples of this, taken from Brandon Hill, gave from 97:4 to 98°a 
per cent. of silica. In places it is used for brick-making, being 
