COAL MEASURES IN THE SOUTH-EAST OF ENGLAND. 227 
that time have told them what their chances were ; nevertheless, 
they state, 44 It does not appear that there has been any actual 
geological investigation or survey of the county of Surrey ; 
therefore it is proper to observe that the non-assignment of coal 
to that county in the maps which profess to give the geological 
character of England is not a matter of importance. The most 
scientific geologists admit that there are various unexplored 
localities which future research may add to the. coal-fields 
already known.” The projectors seem also to have found 
encouragement in the prospect of being able 44 to work a mine 
so near Windsor.” 
While practice has been making during the last two cen- 
turies these tentative efforts — efforts even now continued from 
time to time almost as blindly as in former days* — science in 
the meantime has been making slow but sure advances, and is 
now prepared with an hypothesis respecting the existence of coal 
in our southern counties of very great probability. William 
Smith first established the order of superposition — confirmed 
by succeeding geologists — of the secondary and tertiary rocks 
of the south of England, the thickness of which at their point 
of outcrop in or nearest adjacent to the London basin may be 
roughly estimated as under : — 
Order of Succession of 
Locality of estimated 
Average 
the Strata. 
Thickness. 
Thickness. 
Bagshot Sands 
Surrey 
300ft. 
London Clay 
Middlesex . 
400 
Sands and Mottled Clays 
Surrey 
80 
Chalk . . . “ . 
Hertfordshire 
1000 
Upper Greensand . 
Surrey 
30 
Gault .... 
Surrey 
120 
Lower Greensand . 
Surrey 
500 
Weald Clay and Hastings 
Sands .... 
Sussex 
2000 
Purbeck and Portland Beds Berkshire, Oxfordshire 
~~7or* 
Kimmeridge Clay . 
Buckinghamshire 
450 
Coral Bag, Oxford Clay . 
Wiltshire to Oxfordshire 500 
Oolites .... 
Gloucestershire . 
750 
k Lias .... 
Gloucestershire . 
600 
[ New Bed Sandstone 
Somersetshire . 
800 - 
7,600 
* Even up to the present day a firm belief exists among many, even of 
men experienced in coal-workings, that in the lower tertiary strata between 
the London Clay and the Chalk, good coal exists. As hundreds of wells 
and sections innumerable expose these strata, we well know how futile any 
such expectations, founded on the presence of irregular seams of lignite, are. 
