COAL UNDER SOUTH-EASTERN ENGLAND, 1 47 



No sooner had this important theory, based on reasoning from observed facts, 

 been thoroughly started than the truth of the first part of it, that is the occurrence 

 of old rocks directly beneath the Cretaceous beds of the South-East of England, 

 was absolutely proved. This proof was given by the deep boring at Harwich, 

 which showed the occurrence, at a depth of about 1,015 ^^^^ below Ordnance 

 Datum,-* of Carboniferous rocks, but which are older than the Coal Measures. 



At about the same time further evidence was given by the Kentish Town 

 boring, which reached red and grey beds of doubtful age, but unlike anything 

 Cretaceous or Jurassic, at about 930 feet below Ordnance Datum. 



Other borings in and near London, and all made for water-supply, have con- 

 tinued the proof. In some cases these have shown more of the doubtful red 

 rocks, in others rocks of which the age is clearly marked by the contained fossils, 

 both Devonian and Silurian beds being found. There is no need to enter into 

 details of these deep borings, which have been fully described. Their sites are 

 Richmond, Streatham, and Crossness (on the south of the Thames), Kentish 

 Tovra, Meux's Brewery, Cheshunt, and Ware (on the north of the Thames). 



Besides these, two other deep borings, at Chatham and at Dover Prison, 

 though they have not reached the older rocks, yet give evidence of the under- 

 ground thinning of the Lower Cretaceous and of the LIpper Jurassic beds. 



It should be noted that in some of these borings a thin representation of Lower 

 Jurassic beds comes between the Cretaceous and the older rocks, which last are 

 reached at depths of from about 710 to 1,222 feet below Ordnance Datum. 



From what has been said above it is clear that the question of the presence of 

 a floor of Older Rocks next beneath the Cretaceous beds, or but slightly separated 

 therefrom by Jurassic beds, in South-Eastern England has for some years passed 

 out of the chrysalis stage of theory into the fully-developed stage of fact. A full 

 account of the question has been given in a Geological Survey Memoir (" The 

 Geology of London and of Part of the Thames Valley," vol. i., pp. 10-50, 1889). 

 to which the reader is referred. 



Although the occurrence of a floor of Older Rocks at no enormous depth 

 beneath the surface was soon, proved, geologists were still greatly at variance as to 

 the second part of the theory, the likelihood of the occurrence of Coal Measures. 

 There were not wanting some to contend that Coal Measures would not be 

 found underground in the South-East of England, but that the formation in ques- 

 tion was likely to thin out southward and westward from our known coal-fields. 

 Others, too, held that, should Coal Measures occur in such a position, they would 

 be found to be unprofitable as far as regards containing seams of coal of a work- 

 able character. 



Others, however, who, it always seemed to me, had more reason on their side, 

 pointed to the fact that not only do Coal Measures occur at some depth under- 

 ground on the west, in the Bristol district, and on the east, in Belgium and 

 Northern France ; but that in both cases these hidden Coal Measures yield work- 

 able coal, which, indeed, was and is largely worked. This being the case, it was 

 argued that what had been proved to be the case at either end of the long line of 

 disturbance (from South Wales even to Western Germany) was likely to occur 

 also in the tract between, in which the range and extent of older rocks were little 

 known. 



Strange to say, no attempt to prove the truth of either view was made m 

 England for many years, and all our knowledge was derived from bormgs made 

 4 In this and in the following cases the depth /ro>ri tlie sttrface of course varies according to 

 the level of the site. The figures siven are referred to one level, practically sea-level. 



