SILURIAN, DEYONIAN, AND CARBONIFEROUS ROCKS NEAR LONDON. 293 
Cambrian and Lower Silurian rocks, those which are now known 
by the name of the Longmynd and Harlech, with the succeeding 
Lingula Flags, Tremadoc and Arenig, life groups of antiquity 
so high that we have no formula to express their age. 
We have no evidence yet as to these rocks of highest antiquity 
occurring eastwards of the Pennine axis, of which Charnwood is 
a prolongation; and longitude 1°50' W. limits the easterly surface 
exposure of the lowest Palaeozoic rocks, and these are the Charn- 
wood slates, &c., of yet undetermined age. The problem still 
remains unsolved; but the Ware trial has revealed a group of 
rocks at a depth of 800 feet that shadows forth older rocks still, 
and should the dip of these Hertfordshire Silurians prove to lie to 
the south, we may anticipate the more ancient series further 
north towards Cambridge. Be it remembered that the strike from 
Ware in that case would be directly towards Harwich. The 
four trials are from London due north. At two of these (Ware 
and Turnford) the true direction of the dip will, it is hoped, be 
tested and determined, the solution of which is worthy of all 
experiment and patience. If successful, it will be the key by 
which the hidden structure and wealth of any given area in 
Britain may be tested. 
What are the Old Rocks South of the Thames ? 
Since the determination of the presence of the Devonian rocks 
at Tottenham Court Road, north of the Thames, and the Upper 
Silurian at Ware, 24 miles further north, our views relative to the 
distribution of the Coal Measures have materially altered. It 
would now appear from recent research, that there is little chance 
of any rocks younger than the Devonian occurring due north of 
London, beyond latitude 52° 30' N., or east of longitude 1° W. 
Whatever may be the contour or disposition of the old Devonian 
and Silurian land at from 800 to 1,000 feet deep it is clear that 
all the stratified rocks between the Devonian and the Grault are 
wanting ; in other words, the whole of the Carboniferous series, 
the Permian and Triassic, the Jurassic including the Lias, and 
the Purbeck and Wealden are wanting or missing north of the 
Thames to the latitude above-named. This shows the great 
unconformable overlap upon the Silurian and Devonian floor, 
which became submerged to receive the upper Secondary rocks 
whose outcrop now extends throughout the length of England, 
from Redcar in the north-east to Teignmouth in the south-west, 
and which also fill the great depression which extends from the 
Mersey and the Dee to Burford in Oxfordshire, where it is 756 
feet deep, as proved by the boring. How much further east it 
may extend we know not, but little west of London it seems to 
