292 V. C. ILling—The Search for Oil. 



chief reliance is being placed on the lower portion of the Carboni- 

 ferous system, particularly the porous horizons of the Millstone Grit 

 series and the Carboniferous Limestone. On the other hand, the 

 Coal- Measures and Yoredale Shales, which respectively overlie these 

 porous rocks, will be relied on to form impervious cover-rocks to 

 prevent the oil and gas from escaping during the normal processes of 

 denudation. The next stage in the undertaking is the examination of 

 the tectonics of these Carboniferous rocks and the choosing of areas 

 for drilling operations where the structures are suitable for oil and 

 gas accumulation. Such areas are mainly anticlinal in form with 

 an adequate thickness of undenuded impervious rocks on the crest 

 of the fold. This almost necessarily implies drilling in the Coal- 

 Measure basins on subsidiary anticlines in the main synclines. 

 This restriction in the choice of sites for wells, which is due to 

 the extreme dissection of the Carboniferous rocks in Britain, is in 

 itself a very unfavourable factor. It limits the possible areas for 

 drilling to a*small percentage of the whole area, and localizes the 

 wells on structures which, although themselves favourable, are 

 merely subsidiary portions of larger structures that are distinctly 

 unfavourable. The wells which are being put down in the 

 Chesterfield area are situated on the axis of a sinuous anticline in 

 the main Yorkshire basin ; this anticline runs through Brimington 

 in a northerly direction and then curves westward. Drilling 

 operations are also in progress both in North Staffordshire and 

 Midlothian. 



The evidence which has been brought forward in favour of the 

 possible occurrence of oil-pools in Great Britain may be considered 

 under three heads : — 



1. The indications of petroleum. 



2. The supposed association of oil and carbonaceous strata. 



3. The analogy with the American oilfields. 



The writer proposes to describe and discuss this evidence in an 

 endeavour to estimate the chances of success which await the 

 present drilling operations. 



1. Indications or Petroleum. 



It is natural that prominence should be given to the evidence of 

 asphalt, oil, and gas within the strata of these Islands by those who 

 favour the present project. The occurrences are not uncommon, 

 especially in the Carboniferous system, and apart from the pre- 

 Cambrian and older Palaeozoics, examples appear to have been noted 

 almost throughout the geological column. The rare and local 

 occurrences of bitumen in the pre-Carboniferous rocks of Britain, 

 mainly in the Old Red Sandstone, are of no economic significance, 

 and he would need be more than an optimist who drilled, hig wells 

 within these formations. Throughout the Carboniferous system the 

 evidence of hydrocarbons is more common. Instances of local oil 

 impregnation in the strata of the Calciferous Sandstone series of the 

 Lothians are probably due to destructive distillation of contiguous 

 " oil-shale " by pyrometamorphism. This reaction is essentially 

 similar to the present process of retorting the shale, and a corresponding 



