Ixxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY, [vol. Ixxvii, 



alone, the conclusion would be the opposite, that reversed faults 

 Avere the normal condition and the so-called ' normal ' faults com- 

 paratively rare ; this I find has equally been the experience of some 

 other geologists Avhose detailed field-work has been mainly beyond 

 the British Isles, but as a world-Avide generalization it would 

 probably be as incorrect as the opposite. The real truth appears 

 to be that the prevalent tj'pe of faulting varies in different regions^ 

 and that there is not at present sufficient evidence to show which 

 can be regarded as more frequent and therefore more normal in 

 the ordinary sense of the word, or whether, taking the world as a 

 whole, the one is not about as frequent as the other. 



A few years ago, I had experience of what may be regarded as an 

 instance of the effect of the double meaning of the word ' normal.' 

 At that time I was interested in the amount of the vertical throw 

 of faults, Avhich had demonstrably originated as normal or reversed, 

 in the special geological meaning of these words. The conditions 

 of the enquiry excluded that large group of faults where the 

 inclination from the vertical is so small that a transference from 

 one class to the other might have been produced by tilting 

 subsequent to the formation of the fault ; and of those not so 

 excluded instances of reversed faults with throws of 6000 to 

 10,000 feet were on record, but I could find none of a definitely 

 normal fault of more than about a couple of thousand feet. 

 Yet it would have been dangerous to conclude that the possible 

 limit of vertical throw was markedly less in the case of ' normal ' 

 than of 'reversed' faulting, for the alternative interpretation 

 was equally possible, that, where the fault was normal, the 

 observer saw no reason for emphasizing Avliat might be understood 

 without s])ecial mention ; while, if the fault was reversed, it was 

 a matter for record, as something out of the common. 



In this instance the former interpretation may be the true 

 one, and the limit of possible vertical throw of a definitely normal 

 may be much less than in the case of a definitely reversed fault, 

 or of the intermediate class of those having so small a hade that 

 their original classification is uncertain ; but this question will not 

 be treated here. At present I am not concerned with theories 

 of the origin of faults, but with a consideration of the meaning 

 of the words employed to describe them, and among those 

 having a special meaning in geology, which have abeady been 

 used, we may find examples of the opposite extremes of safety or 

 danger. The word ' hade ' is a good example of the former class. 



