ZONES IN INFERIOR OOLITE SERIES. 37 
Zones. 
The fact that the strata are so variable has naturally influenced 
the assemblages of fossils that characterize particular portions of 
the sea-bed. So that while numerous local divisions may be made 
in the rocks, attempts at minute correlation of particular layers 
are apt to provoke diversity of opinion. Ammonites, however, 
have come to be regarded as " time-keepers," for they appear to 
be less influenced than other Mollusca by the character of the 
sea-bottom. Their distribution at any rate was not hindered by 
such considerations, although the forms were subject to more 
rapid modifications than those of other Mollusca. 
Doubtless there is a tendency at the present day to make more 
and more minute divisions of the strata ; and so long as they are 
taken simply to indicate the local natural history of the beds they 
are useful. What is much more serious is the multiplication of 
the specific names of fossils and especially of the Ammonites ; for 
now-a-days the identification of species has become well-nigh a 
hopeleg.3 task, unless one reverts to the deh'nitions of the older 
palaeontologists. Forms hitherto grouped under definite specific 
names, such as Ammonites Parkinsoni, A. humphriesianus, A. 
Sowerbyi, A. Murchisonce, &c., are so split up that only a specialist 
can recognize the many so-called species or rather " mutations " 
into which they are divided. Their original significance, and 
their historical associations are obscured. Such a proceeding, too, 
tends considerably to modify the interpretation of zones, and to 
render them dependent rather on the occurrence of one of these 
particular forms, than on the faunas or general assemblages of 
fossils with which a species may be associated. In many places 
Ammonites are scarce, and it is known that the occasional presence 
or absence of a so-called zonal species cannot always ba taken as 
definite evidence of the presence or absence of the special horizon 
it may characterize. 
It is true, as has been stated, that the assemblages of fossils 
vary from place to place according, no doubt, to the particular 
sedimentary conditions that suited them, but there are some 
species sufficiently widely distributed to mark the general 
succession in the life-forms of the Inferior Oolite. Whether, 
however, we take a broad or a restricted view of species, there 
is great difficulty in subdividing the Inferior Oolite into definite 
zones, and in tracing these palaeontological divisions throughout 
the country. Probably no other formation has given so mucl/ 
trouble to those who endeavour to parcel our strata into zones.* 
It will be seen that the zones are not marked by any persistent 
lithological characters. Even in Dorsetshire, where Ammonites 
are most abundant, it is remarkable that the zones are nowhere 
all well developed at one locality where they can be studied in 
sequence :t the "fossil-beds" that sometimes represent distinct 
* See also Hudleston, Address to Geol. Soc. 1893, Quart. Journ. Geol. Soc,, 
vol. xlix (Proc.) pp. 129, &c. 
+ Sec Hudleston, luf. Ool. Gasteropoda, p. 23. 
