48 A PROBLEM FOR CHESHIRE GEOLOGISTS. 
period or another since the commencement of the Tertiary, and 
on these submerged areas strata, often of enormous thickness, 
have been deposited ; out of such strata masses like the Rigi 
and Mt. Pilatus have been carved by denudation. Each of the 
great Tertiary systems—the Hocene, the Oligocene, the Miocene, 
the Older Pliocene and the Newer Pliocene—is represented at 
one point or another by strata thousands of feet in thickness. 
It is not necessary, however, to go beyond the limits of 
our own islands in order to find proofs of the great amount 
of denudation which went on during the Tertiary periods. 
Around London we find great masses of water-worn flint 
pebbles (the Oldhaven beds) 50 feet or more in thickness, 
which must represent the destruction of many hundreds of feet 
of Chalk. Still more impressive is the fact that the volcanoes 
of the Western Highlands of Scotland, which in the middle 
portion of the Tertiary period rivalled Etna in height and bulk, 
are now reduced to ‘basal wrecks,’ none of which exceed 
3,000 feet in height. All the existing grand mountain-ranges of 
the globe appear to*have originated in the Tertiary peried, for 
so great is the work of denudation that the older mountain- 
chains have been worn down into insignificant ridges. 
From what has been said, everyone must admit that the 
greatest interest surrounds these isolated patches of Secondary 
strata. By their critical study the geologist is led to entertain 
juster views concerning the past history of the district in which 
they occur, and to acquire more correct notions of the sequence 
of the events which have taken place in successive geological 
periods. 
Now there is situated at no great distance from the City of 
Chester one of these patches of Secondary strata, many of 
the details concerning which require to be carefully worked 
out, in a manner which is only possible for residents in the 
neighbourhood. 
The patch of strata in question is by no means inconsiderable 
in size, for it has a length of from 10 to 12 miles, and a breadth 
of about 4 miles. It is oval in form, lying with its longer axis 
from N.E. to 8. W., between Audlem and Wem. 
The existence of this interesting outlier appears to have been 
first made known to geologists by the late Str RoprErick 
Murcuison, in a short paper in the Proceedings of the 
Geological Society for 1835. 
The Geological-Survey map of this district was published 
in 1855; the attempt to lay down the boundaries of the outlier 
is confessedly an imperfect one, for a geological surveyor visiting 
the district for a short period is at a great disadvantage com- 
pared with the local residents who can utilize every accidental 
opening made during a long course of years. 
