V. C. Tiling— The Search for Oil. 299 



loss by evaporation and seepage is going on in them at the present 

 time, but the geological time has been insufficient for complete 

 leakage, being relatively short compared with the long geological 

 periods of post-Carboniferous history. 



An interesting and instructive example of the great importance 

 of migration in disturbed strata is afforded by the Palaeozoic oilfields 

 of Southern Oklahoma and .Northern Texas. The oil is found 

 mainly in strata of Permian age, the so-called " reel beds ". These rocks 

 are tilted at angles somewhat greater than is usual in Pennsylvania, 

 and they are underlain unconformably by strongly disturbed 

 Carboniferous strata. There are two interesting features about the 

 oil occurrence in these fields to which attention is here directed. 

 Firstly, the common occurrence of asphaltic sandstones .in surface 

 outcrops indicating the petroliferous nature of the underlying strata. 

 Secoudly, the almost certain conclusion that the oil is not indigenous 

 in the Permian formation, but has migrated upwards from the 

 disturbed Carboniferous strata. During this migration some of the 

 oil has evidently escaped to the surface, hence the asphaltic 

 sandstones, but the great thickness of the Permian cover-rock, 

 probably helped by overlying Cretaceous and Tertiary beds now 

 removed, retained large portions of the oil in the strata. 



These features serve to illustrate the two main facts on which 

 stress is laid in the present communication : — 



1. That disturbed strata, especially when strongly faulted, do not 

 easily retain oil over long geological periods owing to the leakage 

 of this somewhat elusive material to the surface. 



2. That when such migration has taken place, or is taking place, 

 the indications of bitumen in the overlying rocks or at the surface 

 are sufficiently obvious to leave no doubt in the mind of the 

 investigator as to the petroleum content of the underlying strata. 



The writer must apologize for a long digression into the occurrence 

 of petroleum in the American Palaeozoic rocks, but such a comparison 

 is necessary seeing that it is among the British Palaeozoics that the 

 search for oil is at present being carried out. The same laws which 

 are necessary for the preservation of oil in the one country should 

 hold good in the other, and the folding, fracturing, and subsequent 

 denudation of the British Carboniferous strata should be compared 

 with that of the same strata in the American oilfields. This 

 comparison will indicate whether it is possible or likely that large 

 quantities of oil still remain in the Carboniferous strata of these 

 Islands. 



It will be noticed that the writer is assuming that the first two 

 essentials, the formation of the oil and its migration to suitable 

 porous reservoirs, have been fulfilled in the case of the British 

 rocks. Such an assumption may in itself be illegitimate, for oil 

 formation on a large scale requires special geological conditions. 

 Whether these conditions were fulfilled during the deposition of 

 any of the sedimentary formations in the British Isles must be 

 largely a matter of opinion, but it is quite probable that such has 

 been the case. Apart from the Carboniferous rocks in the South of 

 England, Wales, and Ireland, these strata elsewhere escaped the 



