38 
LOWER OOLITIC ROCKS OF ENGLAND: 
horizons occurring here and there at different spots Moreover, 
in this and other areas, as at Dundry, there is sometimes a 
commingling of certain zonal species, that renders it impossible to 
draw rigid planes of division. Where the beds are very thin it 
may be that the sediment was insufficient (as remarked by Tawney 
in reference to the Lias of Radstock) to bury up the organic 
remains of successive stages.* 
It is interesting to note the different minor divisions in 
different localities, but considering all the facts and the many 
varieties of opinion, it is best to adhere to broad general 
groupings, which may be made with a fair approximation to 
truth, instead of attempting to correlate the minor divisions, 
many of which of course are impersistent, and often unfossiliferous. 
It will be desirable now to mention the species that are 
considered more particularly to characterize the different stages 
of the Inferior Oolite Series. Many of these are not confined to 
particular zones, and their distribution or abundance varies in 
different parts of the country. 
It will be sufficient for our purpose to adopt the following 
general divisions of the strata, premising that the zones in the 
midland counties are not well established : 
TABLE OF THE CHIEF SUBDIVISIONS OF THE INFERIOR 
OOLITE SERIES. 
Upper 
Lias, 
Zones. 
S.W. England. 
Midland Counties. 
Ammonites Parkinson! 
A. humphriesianus (in S.W. 
England). 
Inferior Oolite. 
Lincolnshire Limestone. 
Collyweston Slate. 
Lower Estuarine Seriei. 
A. opalinus 
Northampton Sand. 
A . jurensis 
MiQiord band. 
* See Memoir on the Lias, p. 127, and Proc. Geol. Assoc., vol. xii. p. 803. 
