VoL. XIV.(2) THE PRESIDENT’S ADDRESS 93 
described is illustrated in the gorge of the Avon at Clifton, 
and at Skrinkle, near Tenby. Microscopic sections of 
corresponding beds in the Forest of Dean also show them 
to be full of remains of organisms. Some of the beds are 
little other than accumulations of the valves of Ostracoda. 
In other remains Polyzoa, Corals, shells, ossicles of 
Crinoids and granules of Mitcheldeania are the chief 
features. 
Stage B represents either a deeper water condition or 
clearer water. It is true that at Clifton the base of the 
Middle Series is represented by an alternation of lime- 
stones and shales which terminate in dark limestone full 
of microscopic life, of the exact nature of which we are at 
present ignorant. This series of beds I have termed the 
“ VMitcheldeania Beds,” * from the fossil organism Mztchel- 
deania being characteristic of the limestone, a term which 
is generally accepted. Above the Mitcheldeanta-series 
comes the great mass of the limestones represented in 
Stage B. The chief feature of them is that they are largely 
made up of the tests of Foraminifera, or the ooze which 
was deposited on the floor of the Carboniferous sea, 
resembling that now forming at the present time over 
certain areas of the sea-floor. 
Stage C is, to a certain extent, a repetition of Stage AS 
that is, the limestones become mixed with sandstones and 
shales, and finally give place to the Millstone Grit, to 
which reference has been made. At intervals throughout 
the formation the limestone becomes what is termed 
dolomitised; a chemical change took place, obliterating, 
for the most part, the original structure of the rock and a 
double carbonate of limestone and magnesia was formed. 
This is the mineral dolomite, which is noticed at several 
horizons at Clifton and Tenby ; and in the Forest of Dean 
practically the whole of the strata in Stage B has been 
1 Quart. Journ, Geol, Soc., Vol. xliv. pp. 186-199. 
