FOSSILS OF THE OOLITIC SERIES. 23 
Plant-remains occur conspicuously in the Lower Purbeck Beds, 
and occasionally at other horizons, as in the Stonesfield Slate. 
The collector must bear in mind that many localities regarded 
as specially fossiliferous, owe their celebrity to the energy ot 
resident geologists. Thus Minchinhampton, which furnished 
Dr. Lycett with so many treasures from the Great Oolite, yielded 
them only after much toil and time and money had been 
expended. 
Attention has already been drawn to the subject of Zones, so 
that a more particular consideration of them may be reserved for 
discussion in connection with the several stratigraphical divisions. 
Strictly speaking, Zones must be named from forms that are 
wide-spread, and only an extended knowledge can justify their 
introduction. Vague as the limits of Zones must necessarily be ; 
they are naturally better represented in a series of clays, than in 
the false-bedded oolites. 
In addition to Ammonites, Belemnites and Brachiopods many 
species of which are wide-spread, there are other forms of life 
that are useful locally to mark horizons. They are rather 
-to be considered as characteristic fossils than as zonal species. 
Thus some species of Avicula, Gryphaa, Trigonia, of Echinoids 
and other fossils, serve locally to indicate horizons in the Oolitic 
rocks ; but while a number of the species appear to be thus 
restricted, other species of the same genera have a considerable 
duration in time. 
Prof. Phillips devoted much attention to the subject of the 
succession of various life-forms,* and the accompanying Table 
will serve to illustrate some of the species that may thus be 
selected as characteristic of, though not in all cases confined to, 
particular stages. 
* Geology of Oxford, &c , p. 399 ; see also IT. B. W., Proc. Geol. Assoc., vol. xii. 
p. 305. 
