Ixxxiv PEOCEEDI^GS OP THE GEOLOGICAL SOClEXr. [.Juue I912, 



and that there is no sign, or even likelihood, of the existence 

 of a similar buried fold under the Xeozoic rocks. To meet this 

 objection, it may be wise to subtract a third from the provisional 

 estimate just made ; and, if that is done, the area of possible buried 

 €'oal-measures Avould be reduced to about 2700 square miles. 



There exists, of course, the Wealdeu anticline with whatever 

 folding may underlie it ; but as there is always the possibility that 

 the southern limb of such folds will bear rocks of the Devon 

 type, it must be left outside our consideration on the same principle 

 that the exposed Carboniferous area of Devon has itself been 

 ignored. 



It is necessary to point out that the figures last given are merely 

 the expression of arithmetical and not of geological probability. 

 It would be much more satisfactory if we could substitute the latter 

 for the former ; but, in view of the present insufficiency of infor- 

 mation as to structure of the concealed area, no geological estimate 

 in the form of figures can be made. 



(c) Conditions of Cover and Structure. 



In dealing with this buried area of Palaeozoic rocks, its possible 

 -content of coal-basins, and the probability that they may be worked 

 Avith profit, there are three factors to be taken into account: — 

 (1) The thickness of the unconformable cover ; (2) the general 

 structures of the concealed Palaeozoic rocks on a large scale, the 

 -greater folds or faults by which they may be traversed, and the 

 resulting geographical distribution of the outcrops of different 

 members of the Pakisozoic group ; and (3) the detailed structure of 

 the Carboniferous areas, and the presence of conditions which may 

 or may not render it possible to work them profitably. It is hardly 

 possible to treat these branches of enquiry quite separately, as they 

 ■overlap one another, as also does the evidence on which our know- 

 ledge of them depends. 



We possess a certain amount of information as to the directions 

 in which variations in thickness of cover tend to occur. This 

 is partly derived from general principles worked out from surface 

 outcrops, but it is mainly dependent upon the direct evidence 

 yielded by actual borings. Thus, other things being equal, the 

 thickness may be expected to increase on the whole towards the 

 centre of the synclines by which the newer rocks are affected. In 

 spite of this knowledge, remarkable and unexpected variations are 

 now and then brought to light, like the great thickness of certain 



