the seventeenth century. "The Rev. Giles Thornborough, one of his Majesty's chaplains, digging a boring for coal in Slyfield Green, found, first of sand and gravel 7 ft.; then a spring; within a little of that a bed of stones like square caps and about 2 ft. every way, on the outside whitish, within full of sulphur, out of which was extracted tinn by L. Smyth, of London, engraver. These stones are called at the coal pits at Newcastle,' catts' heads,' lying always (they say) where coal is. These catts' heads are all full of small pipes for the mine to breathe through. Next under them lay a body of black clay for 15 fathoms; then a rock of stone about a yard thick, which was very hard. Then they came to black clay again for about 3 fathoms, and then another rock; after that, clay mixed with minerals (of which Prince Rupert hath some, as also had King Charles in his closet, which was there placed by the Indian oar); then cockle shells, muscle shells, and periwincle shells, some filled with oar (out of which Prince Rupert extracted tinn and other things), and some filled with clay. After this sprung a bed of oker, 12 ft. thick, a kind of mother-of-pearl; after that, a green quicksand. Then came coal, which how deep it is, is unknown, for here the irons broke: thought by Mr. W. Lilly (astrologer) to be subterraneous spirits; for, as fast as the irons were put in, they would snap off. This is a kind of rocky coal (like that which they call Kennell coal) which burns like a candle." Mr. Thornborough was induced to make this trial, because "there was a kind of stony coal (lignite) that would burn, which he found by grubbing up the roots of an old oak in his ground there." After spending 400l. the work was abandoned, to be however revived again about a century and a half later, in the neighbourhood of Worplesdon.

The Wealden strata at Bexhill in Sussex consist of a series of sandstones, clays, and lignites, which led in 1804 to an expensive trial for coal near that village. A shaft was sunk to the depth of 164 ft., and two seams of lignite, designated as smut coal, 2 ft., and strong coal, 3 ft. thick, were met with. The reputed resemblance to coal measures was kept up by the use of such terms as "church clay," "grey bind,” “blue bind with iron ore," &c., and the presence of a seam of clay with impressions of wealden ferns not unnaturally assisted the delusion. Fortunately probably for the company, the mine was drowned out, and stopped the further extension of the work.

So recently as about thirty years since, another attempt was made to get up a company to establish a colliery at Worplesdon, near Woking, in the Bagshot Sands, and to sink a shaft to the depth of 150 ft. At that depth the projectors would have reached the London clay; but it is certain that no more profitable material would have rewarded their outlay. Any geologist could at

that time have told them what their chances were; nevertheless, they state, "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 "to work a mine so near Windsor."

While practice has been making during the last two centuries 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:

Sands and Mottled Clays

Chalk

Upper Greensand
Gault

Weald Clay and Hastings

Sands.

Lower Greensand

Purbeck and Portland Beds Berkshire, Oxfordshire

Kimmeridge Clay

Coral Rag, Oxford Clay.

Oolites

Lias

{New Red Sandstone

Buckinghamshire

Wiltshire to Oxfordshire 500

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.

And since then the order of the older underlying rocks has been thus determined by Sir R. Murchison, Professor Sedgwick, and others :

It was for a time supposed that secondary strata maintained in the main their regular sequence and thickness unimpaired over large areas, and in our early geological works the section of the secondary formations, from the west to the east of England, is given as under:

In this case, the depth to the coal measures under London, supposing they existed there, would have been from 7,000 to 8,000 ft. or more. Speculation was hushed in presence of such depths, nor did it actively revive until the facts more recently acquired showed that the obstacles presented by such an enormous mass of strata had no real existence.

Admitting the variation of thickness, we were hardly, however, until lately, prepared to admit how rapid that variation was. Professor Hull has shown that the Lias and Oolites become much thinner as they range eastward from Gloucestershire. There is reason to believe, in fact, that the oolitic series do not extend far under the chalk hills of Berkshire, and it is known that the Inferior Colite thins out even before reaching Oxford. Mr. Hull gives a section, from Gloucestershire (the neighbourhood of Cheltenham) to Oxford, in which he shows that all the rocks below the Great Oolite thin out rapidly to the south-east;

and he estimates the thickness of the whole at Oxford at about 600 ft., whereas in Gloucestershire it is 1,880 ft. :

To the north-eastward the Great Oolite and the Oxford Clay become but slightly thinner. On the other hand, the Kimmeridge clay, which is 275 ft. thick at Swindon, is 310 ft. near Abingdon, and increases to 450 ft. at Aylesbury. In like manner, the Portland and Purbeck series increase from 12 to 70 ft.; while the Wealden series, which is altogether absent in. the west of England, is about 2,000 ft. thick in Surrey and. Sussex. So the Lower Greensand, which is only 50 ft. near Devizes, attains a thickness of about 500 ft. at Reigate. The Gault maintains a mean thickness of about 100 ft.; while the Upper Greensand, 150 ft. thick at Devizes, is reduced to 25 ft.. at Merstham. The Chalk, taken at its full development, maintains tolerably constant dimensions from Wiltshire to Dover, viz. of from 800 to 1,000 ft. unless when, as often happens, it has suffered denudation. Notwithstanding, therefore, the large development of the Secondary formations, both westward and northward of the London basin, it was uncertain how many and how much of these might be found to extend under the Tertiary strata of the south-east of England. We did not anticipate, however, the great hiatus which in reality has been found to exist. Whatever might be the case with the triassic and jurassic series, it seemed at all events probable that the lower cretaceous strata, which are so fully developed a few miles both on the north and south of London, would, like the upper cretaceous strata (the chalk), pass under London, and therefore it was a matter of surprise when the boring at Kentish Town, made in 1854, showed that not only were the older secondary strata all absent, but also the lower greensands, which are so well developed in adjoining parts of Kent and Buckinghamshire. In the place of the latter were found a series of red and grey sandstones belonging probably to the Old Red Sandstone, so that the following diagram (fig. 2) may now be considered as representing probably the order of succession and position of the strata from the West of England to London :

In the same way MM. Dufresnoy and Elie de Beaumont*

"Explication de la Carte Géologique de la France, 1841," vol. i. p. 727.

have given a diagram showing a similar thinning out and overlapping of the strata from south to north in the north of France, and a like unconformable independence of the secondary

and of the paleozoic series, only there the older strata come to the surface, which they do not in south-eastern England :

a

FIG. 3.

N

f

d

Westward of this line of diagram in France, the palæozoic rocks sink deeper, and are altogether covered by secondary and tertiary strata; and while at Lille the chalk is found to repose on the mountain limestone, at Valenciennes it reposes on coal These latter are the prolongation of the great Belgian coal-field, which ranges from Liège westward to and .beyond Mons.

measures.

It is about two centuries ago that the Belgian coal-basin was found to pass beneath the newer formations westwards in the direction of France, where the Coal Measures were supposed to be lost under these Cretaceous and Tertiary strata. It occurred, however, to some more far-seeing men that they might possibly be recovered, and, after various trials, their search was attended with success, the strike of the coal measures hit upon, and valuable collieries established at Anzin and Aniche, in the neighbourhood of Valenciennes. This encouraged further search, and the coal measures have been gradually followed in a westerly direction under the chalk to within thirty miles of Calais, and at that town a boring for water, made by M. Mulot in 1842, proved the presence of carboniferous strata (but not the coal measures) under the