part 1] ANNIYEBSARY ADDRESS OF THE PRESIDENT. IxXVU 



rNnei :seatton. 



' Know your" Faults.' 



Custom has decreed that on these occasions your President shall 

 deliver an address, which is usually devoted to a review of the past 

 history, of the present condition, or of the future needs of some 

 •department of Geological Science. To-day I propose to follow 

 neither of these courses, but to make a digression into the 

 j)hilosophy of our science, to examine the meaning of some of 

 the words which we use, and to take for my text that motto 

 which, blazoned in letters of gold from the ancient temple of 

 Delphi, may be translated by geologists as ' know your faults.' 



Faults there are, and many, of observation, of description, of 

 interpretation, but they will only be considered in connexion with 

 faults in the technical meaning of f i-actures of rock, along which 

 movement of the opposite sides has taken place. These, as the 

 text- books tell us, are of two kinds, normal or reversed; the classi- 

 Hcation arose in the coaltields of England, where the phenomenon 

 Avas first studied in detail, and where, with few exceptions, the 

 hade of the fault is towards the downthrow, so that it was natural 

 to regard this as the normal condition, and a ' norinal ' fault was 

 synon^'mous with one in which the hade was toAvards the down- 

 throw, the exceptional cases in which the reverse condition of a 

 hade towards the upthrow Avas found being distinguished as 

 * reversed.' 



So lono^ as the nomenclature Avas conlined to the re2:ion in which 

 it originated, or so long as the purely geological connotation of 

 the words was remembered, no harm could result from the terms 

 made use of ; but thought is by no means free, it is trammelled 

 by the limitation of the human intellect and the impossibility of 

 omniscience, by limitation of our vocabulary, and also by the 

 A'^ariation in the meaning of words, according to their context 

 or the occasion on which they are used. As a consequence of 

 this, the ' normal ' fault came to be regarded as normal in the 

 untechnical sense of the word ; the generalization Avas extended 

 from the district in which it originated to the Avorld at large, 

 and text-books, even those of quite recent date, are found in- 

 sisting on the prevalence of ' normal ' faults and the rarity of 

 reversed ones — yet it is very doubtful Avhether any such disparity 

 of frequency really exists. Were 1 to draw on my own experienc 



