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the greatest variety, and, being classic ground, contains a larger proportion 
of the type forms of the rocks. The development is very unequal, and the 
entire group is reduced to less than 25 feet in some places ; hut where the 
sandy base is expanded, as in those districts where the escarpment faces the 
north, the thickness exceeds 100 feet, occasionally falling to about 30 feet 
in the direction of the dip, with the probability of the entire mass ultimately 
thinning to a feather edge. In many places true Coral Rag is largely 
developed, usually terminating the Corallian series in an upward direction, 
or at most succeeded by a very few feet of ferruginous sand. Throughout 
the great escarpment facing the upper valley of the Thames the lower arena- 
ceous member predominates, though much mixed with thin-bedded sandy 
clays, the whole constituting a loose formation, which is capped by hard 
gritty limestone containing an abundant fauna, representative of the middle 
series, differing somewhat, on the one hand, from the Rag, with its partially 
Kimmeridgian character, and, on the other, from the Lower Calcareous Grit, 
whose affinities are, of course, Oxfordian. The beds of this district, however, 
are exceedingly varied. District IV. includes the Coral reef at Upware, 75 
miles E.N.E. of Oxford; though the exposures are small, they are very sug- 
gestive. The limestone of the south pit is an excellent Coral Rag, but softer 
and more chalky than much of the Coral Rag of the West Midland district. 
Moreover, whilst the rock contains many familiar forms, and especially 
Cidaris Jlorigemma, whose presence in abundance invariably indicates a dis- 
tinct horizon, we also find the casts of shells, rarely or never met with in the 
West of England, but which appear common in some parts of the Continent, 
e.g. species of Isoarca , and certain species of Opts, which latter occur also 
in a portion of the Yorkshire Basin (V.) This bears 130 miles N. by W. 
from the reef at Upware. The Corallian beds are grouped as a belt of rocks 
enclosing an oval tract of Kimmeridge Clay. There is more symmetry 
here than in the south, and the triple division of grit, limestone, and grit, 
though not absolutely true in all places, is fairly accurate ; most of the beds 
are better developed, and the contrast between the Coral Rag and under- 
lying Oolites is strongly marked. In the Tabular Hills these Oolites con- 
stitute a double series, divided by a “ Middle Calc Grit,” a fact first indicated 
on stratigraphical grounds by Mr. Fox Strangways, and amply borne out by 
fossil contents. The shell beds of the Lower Limestones are, especially in 
their lower parts, charged with Brachiopoda and other forms of the Lower 
Calc Grit ; whilst the Upper Oolite, on which the Coral Rag reposes, con- 
tains a far more varied fauna, though singularly destitute of Brachiopoda. 
The fauna of the Rag here, as elsewhere, inclines to Kimmeridgian types. 
In conclusion it was shown that, since the leading feature of the rock masses, 
between the Oxford and Kimmeridge Clays is variety , a strict and rigid 
correlation is altogether impossible. Yet in spite of great local differences, 
producing in many places a strangely contrasted facies, there are certain 
features which may be deemed fairly characteristic of the several divisions. 
The bank-like character of most of these beds is very striking. 
Possible displacement of the Earth's Axis. — In connection with certain 
well-known geological and especially palaeontological phenomena, there has 
long been a growing belief among naturalists that some means must be 
found of explaining a change in the position of various parts of the earth’s 
