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tertiary strata and the chalk, to a depth of 1,138 ft.* Again, under the same strata at Ostend, palæozoic rocks have been discovered at a depth of 985 ft. On the English coast, a boring for water was carried at Harwich to a depth of 1,070 ft., also through tertiary strata and chalk, which were found to repose upon a fossiliferous slate belonging to one of the lower members of the carboniferous series. We can thus follow at intervals the same Tertiary and Secondary strata overlying unconformably Palæozoic strata from Mons to London. The order of superposition and ascertained thickness of the several overlying formations and the nature of the fundamental rock at these points, is shown in the following table :—

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There is little doubt from all we now know that, owing to the absence of all the lower secondary formations the great Tertiary and Chalk plains of Belgium and French Flanders repose directly upon a floor of old Palæozoic rocks, and that a like structure obtains in the London basin, at all events as far as London. The reasons we have for believing that the coal measures are associated with this paleozoic base, we will give further on.

In England, south of a line drawn from Bath to Stamford and Yarmouth, no true coal has yet been found. The whole area is occupied by strata newer than the Coal Measures, commencing with the Liassic and Oolitic series to the east of Bath, and ending with the Chalk and Tertiary series of the neighbourhood of London. Nevertheless, in consequence of certain presumed relations between the coal-fields of Belgium and of

• "The Water-bearing Strata around London," p. 208.

"Bull. Soc. Paléont. de Belgique," Antwerp, 1859. At Vilvorde, near Brussels, Silurian or Devonian rocks were also met with at a depth of about 600 feet.

Calais

Hames, near
Calais

Anzin, near
Valenciennes

Flines Nord

Ville Ponveraeul,

near Mons

the north of France with those of South Wales and Somersetshire, an opinion has for some time prevailed amongst geologists that coal probably exists in parts beneath the newer formations of the south of England.

So long since as 1826, Dr. Buckland and Mr. Conybeare, in their excellent account of the Bristol coal-field, * made the following remarks: "Before we close this general account of the south-western coal district of England, we are desirous of noticing its resemblance in geological structure and picturesque features to the country extending along the Meuse between Namur and Liège. There also we are presented with coal basins encircled by Mountain Limestone, and based on Old Red Sandstone, which latter is displayed at Huy. These rocks are all highly inclined, and are covered by overlying formations. The defiles of the Sambre and Meuse present exact counterparts to those of the Avon and Wye." The relation of the two areas was more particularly noticed in the work just quoted (pp. 724-5) by the eminent geologists MM. Dufresnoy and Elie de Beaumont, who thus express themselves on the theoretical question of the original extent of the coal-fields of Belgium and the north of France, and on their probable range:-"The portions of carboniferous strata, which we have reserved as the subject of the last parts of this chapter, contrast in an important manner with those which we have hitherto described, inasmuch as they do not exhibit the characters of deposits formed in circumscribed basins; all indicating, on the contrary, that they have been deposited in an open sea. From the Ardennes on to the mountains of Wales and Scotland, there extended at that period the bays of a sea, in which the Mountain Limestone was formed, which contains a large number of marine remains, and after that the coal measures of the north of Belgium and a part of England."

"This difference in the character of the two classes of basins of the coal measures of which we have just spoken, is not only an interesting fact for science, but it concerns also in a great degree the future of mineral industry, from the views it may suggest relative to the possible subterranean connection between certain basins. In fact, the deposits formed in circumscribed basins present but little chance of their being prolonged for any considerable distance beneath more modern deposits, but the deposits formed in marine basins are generally much more uniform, and susceptible of much greater extension, when they have not been broken up and destroyed."

• "Geological Transactions," vol. i. pl. 2, 2nd ser. p. 220.

Again, M. Mengy, in 1852,* remarks: "However it may be, the considerable thickness of the overlying unproductive strata (terrains morts) which exist in the western part of Belgium and Department du Nord, shows that there is a great depression there, which is a prolongation of the deep subterranean substrata above which London stands, and if a coal measure basin exists there, which is not impossible, they may extend to the southern border of that depression, which reaches near to Lille, and may be connected more or less directly with the vast carboniferous system which comes to the surface in England, ranging from Wales to Scotland."

But it was not until 1855, when Mr. Godwin-Austen † brought the question before the Geological Society in an able and elaborate paper, accompanied by a map, in which he showed that the coal measures which thin out under the chalk near Théronanne probably set in again at or near Calais, and are prolonged (beneath the tertiary strata and the chalk) in the line of the Thames Valley, parallel with the North Downs, and continue thence under the valley of the Kennet, into the Bath and Bristol coal area, that the attention of geologists was scriously directed to the subject. Reasoning also on theoretical considerations connected with the extension of the old coalgrowth in the west of Europe, Mr. Godwin-Austen concluded that "coal measures might possibly extend beneath the southeastern part of England," and he showed, upon well-considered theoretical grounds, that the coal measures of a large portion of England, France, and Belgium were once probably continuous, and that the present coal-fields were merely fragments of a great original deposit, which he inferred had been broken up in two directions previously to the deposition of the secondary rocks. He endorsed also the opinion that the main line of disturbance had a general east and west direction-that part of it formed the great anticlinal of the Ardennes, by which the Belgian coal-field had been tilted up, and brought to the surface and that the Mendips with the Somerset coal-field are on the same line of strike.

These views have been controverted by some distinguished geologists, but they have received the assent of a greater number; and the information we have since acquired of the thickness of the secondary strata and of the existence of palæozoic rocks at Kentish Town and Harwich,‡ and the discussion

• "Essai de Géologie Pratique sur la Flandre Français,” 1852, p. 76. + "Quart. Journ. Geol. Soc.," vol. xii. p. 83.

For detailed particulars of the strata at these wells, see the papers by the writer in "Journ. Geol. Soc.," vol. xii. p. 6, and vol. xiv. p. 249.

of the subject by the Royal Coal Commission,* enables us now to investigate the physical problems with still greater certainty.

It is evident from what we have already said that the age and position of the surface rocks afford no criterion of the thickness of the strata intervening between that surface and the palæozoic rocks underlying the Tertiary and Secondary strata of the south of England; while it is also clear that the relation of the secondary and of the paleozoic group of rocks to one another is perfectly independent, and that the latter must be viewed entirely on their own internal evidence, apart from the bearing of the newer rocks which cover them unconformably.

A glance at the geological map of Europe will show that the Belgian coal-field is but part of a series of great coalfields ranging from Westphalia to the north of France. These coal-fields are deep, long, and narrow, and their longer axes succeed one to another on the same line of strike.* Omitting a few small unimportant coal-basins, the most easterly of the great coal-fields is known as that of the Ruhr, the second as that of Aix-la-Chapelle, the third as that of Liège, and the fourth as that of Hainaut and Valenciennes. In all these districts the Coal Measures are tilted up or faulted on the south against the Mountain Limestone or the Devonian rocks, or pass northward under Cretaceous and Tertiary strata, beneath which they are prolonged until thrown out by other undulations of the older rocks. The width, north and south, of these coal-fields is always small compared to their length. Thus the coal-field of Liège is only 3 to 8 miles wide, whereas it has a length of 45 miles. So the exposed coal-field of Hainaut, from Namur to beyond Charleroi, is 33 miles long; it then passes under the Cretaceous and Tertiary strata, and is prolonged, with a few small exposures, underground, by Mons to Valenciennes. The length of this other underground portion of the coal-field is 32 miles, making a total of 65 miles, with a width near Namur

Vol. of Evidence taken before Committee D, and Report to that Committee "on the Probabilities of finding Coal in the South of England" by the writer; Royal Commission on Coal Supply, 1871. Free use is made in this paper of this report and also of the writer's anniversary address to the Geological Society for 1872.

†These are given generally in the map, Pl. LXXXV., the main features of which are copied from Dumont's Geological Map of Europe. To them are added the ascertained range of the Coal Measures under the Chalk of the North of France and their probable range under the South of England. To this I have added a series of hypothetical sections along the line of the coal trough and across it, showing the possible disposition of the Coal Measures and the thickness of the overlying strata.

of 2 miles, increasing to 7 or 8 miles near Charleroi, and continued in France with a width of from 6 to 7 miles, where it has been followed under the chalk to within 30 miles of Calais, and there thins out.

Connected with these coal-fields a great line of disturbance, affecting the palæozoic rocks, has been traced from Westphalia through Belgium to northern France, and it is on the northern flanks of the older rocks of the Ardennes range of hills, which have been formed by this disturbance, that the coal-fields of Belgium lie. The same line of disturbance is again exhibited in the Mendips, and is prolonged even as far as the south of Ireland.

In England and South Wales a similar set of phenomena are met with at this other end of the axis of elevation. From Milford Haven to Tenby, contorted strata of the Mountain Limestone and Old Red Sandstone are flanked on the north by the highly-disturbed Pembrokeshire coal-field, which is 24 miles long by 3 to 6 miles broad. The great coal-field of South Wales is 60 miles long by 15 to 18 miles broad; whilst that of Somerset and Gloucestershire (or Bristol and Bath) shows a length in the direction of the axis of the Mendips of about 12 miles, and in the other direction it measures 26 miles.

The Coal Measures of South Wales are not covered by secondary strata, but a large portion of the Somersetshire coal measures are overlaid by some of the lower Secondary rocks, which in their turn pass a few miles to the eastward under the Chalk. At Clandown, near Bath, the Coal Measures are worked beneath 360 feet of Lias and New Red Sandstone, and they have been followed under these superincumbent strata for a distance of 5 to 6 miles from their outcrop, where they are at a depth of about 500 ft. beneath the surface. But between this point and the well at Kentish Town, no trial for coal or water has been carried to the base of the secondary rocks, or has reached more than about 600 ft. beneath the sea level, and the whole area extending to the channel is occupied by upper Secondary or by Tertiary strata.

There can, however, be little doubt of the continuity of the range of the palæozoic rocks under these newer formations from Belgium to Somerset ; but whether or not the Coal Measures were ever continuous between the two districts; and whether, if they were, they have been removed by denudation, leaving only the lower paleozoic rocks, requires further discussion.

So far as the identity of any particular bed of coal or of rock may serve to establish a correlation between the coal measures of Bristol and South Wales and those of France and Belgium, it is not possible, nor should we expect it; for the variation in

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