June i, 1916] 



NATURE 



293 



Measures into synclines and anticlines. It followed 

 that the newer strata were not parallel to the older, 

 and might rest upon any part of the Coal Measures, 

 or even upon any older formation. Surface observa- 

 tions made upon the newer formations gave little clue 

 to the structure of the Coal Measures ; reliance had 

 to be placed on boreholes, and on the identification of 

 the specimens obtained from them. The section there- 

 fore had been drawn through a borehole at Oxton, 

 and near the Annesley Colliery now working, to a 

 borehole at Kelham. 



The Oxton borehole was put down 75 miles within 

 the margin of the concealed coal-field, and proved that 

 the base of the newer formations had descended east- 

 wards 790 ft. in that distance— that is, at the rate of 

 I in 50. The dip of the Coal Measures was rather 

 steeper, and it seemed possible that 

 the coal-field might extend an in- 

 definite distance eastwards, though 

 it might descend to an inaccessible 

 depth. 



The Kelham borehole was put 

 down nearly ten miles east of the 

 Oxton borehole, and proved that the 

 eastward dip of the newer formations 

 was maintained at the same gentle 

 angle. At a depth of a little more 

 than 1500 ft. it traversed a seam of 

 coal, the identity of which was in 

 doubt. At about 1700 ft. it passed 

 through a dyke of igneous rock 

 which was of no significance. More 

 important was the fact that down to 

 about 2400 ft. it was in strata which, 

 by their character and fossils, could 

 be identified as Lower Coal Measures, 

 that below them it met little more 

 than 200 ft. of Millstone Grit, and 

 that it then entered Carboniferous 

 Limestone. 



The greater part of the Millstone 

 Grit appeared to be cut out by a 

 fault, but whatever explanation was 

 adopted, and whatever the coal-seam 

 might be — whether the Top Hard, as 

 supposed by some, or the Silkstone, 

 as appeared more likely — an eastward 

 rise of the Coal Measures had been 

 proved to exist. The deepest part of 

 the concealed coal-field had been 

 passed, and the eastern limit was in 

 sight. 



Similar explorations were being 

 carried on across other parts of the 

 concealed coal-field,* and the result 

 had been to show that the eastern 

 limit lay not far east of the valley 

 of the Trent. Though not so 

 peared possible to the Commission 



ous faults tended on the whole to counteract the dip and 

 to keep the seams within reach. The upper measures 

 were distinguishable into three groups, and the recog- 

 nition of these groups at their outcrops rendered pos- 

 sible estimates of depth to the productive measures 

 below. The results of recent work had been to show- 

 that the outcrops were repeated — that is, that the 

 counteraction of dip by faults was continued in the 

 areas not yet proved by underground workings. 

 Nothing was yet known of the area overlain by New 

 Red Sandstone, 



The Kent coal-field, the third example selected, was 

 wholly concealed by a blanket of Tertiary and 

 Secondary strata, with an average thickness of 1000 ft. 

 towards the north, but increasing to upwards of 

 1700 ft. southwards. The structure of the Palaeozoic 



,Herr» 



RAMSGATE 



.Braboume 



VtrlK^tSc^^ J 



Fig. 2. — Contour-Knes in the surface of the Carboniferous Limestone under Kent. 



large as ap- 

 of 1905, this 

 extension was a notable additioh to the visible coal- 

 field, but its productiveness was still a matter of doubt. 

 Observations on the thickness of coal-seams were 

 difficult in boreholes, but so far the results had been 

 disquieting. 



As a second example, the Denbighshire concealed 

 coal-field was selected. Here it was not so much the 

 existence as the accessibility of the coal-seams which 

 was in question, and the reason was found in a great 

 development of upper measures, for the most part 

 barren of good coal. The dip of the strata was much 

 steeper than in Nottinghamshire, and would speedily 

 carry the seams to an inaccessible depth. But the numer- 



- An account of the investigation as a whole appears in " The Concealed 

 Coal-field of Yorkshire and Nottinghamshire " (Mem. Geol. Survey), 1913. 



floor upon which this blanket rested had been ascer- 

 tained by boring. It had been shown that the Coal 

 Measures existed in a syncline formed in the Carbon- 

 iferous Limestone (Fig. 2). The synclinal axis ranged 

 a little west of north, and the trough became shallower 

 in that direction. Southwards, on the other hand, 

 it deepened and widened, in a manner which suggested 

 that a large part of the coal-field wx)uld lie under the 

 sea. The limestone-surface had been reached in so 

 many borings that it had been possible to draw contour- 

 lines upon it, ranging from 1000 ft. to 3500 ft. below 

 sea-level (Fig. 2). These lines showed that the slope of 

 the limestone-surface, though somewhat steeper on the 

 eastern than on the western side of the trough, was 

 generally gentle. The thickness of Coal Measures in 

 part of the trough had been proved to exceed 2700 ft. 

 The relations of the Kent coal-field to those of the 



NO. 2431, VOL. 97} 



