W. T. Blanford—On Fanlls in Strata. 117 



For these reasons I believe thai. iVictiou-surfaccs in faults rarely 

 exist, and can still more rarely bo seen ; and I believe a lalse prin- 

 ciple will be introduced into geological surveying if their existence 

 be demanded as the only direct jiroof of faulting. 



The next point upon which I differ from my friend is the confusion 

 which, in his opinion, exists between lines of fault and abrupt 

 boundaries caused by deposition against steep surfaces of older rocks. 

 In my opinion these can but rarely be mistaken for each other, and 

 for this reason ; — 



Scarps and cliffs, throughout the world, rarely, if ever, are either 

 straight or composed of a series of straight lines. Almost invariably 

 they are much curved, indented, and cut back every here and there 

 by valleys. Now the essential character of a fault is that its direc- 

 tion approaches a sti-aight line, or is formed of a number of straight 

 lines meeting each other at angles, usually open or obtuse, rarely or 

 never in deep curves. The straightness of a line of boundary is, I 

 think, by most geologists considered far more important evidence of 

 faulting than friction surfaces ; and it has the enormous advantage of 

 being more easily demonstrated. Now this most important point is 

 entirely omitted by Mr. Medlicott, who does not even refer to it ; and 

 yet it is by this character that the great abrupt lines of boundary, 

 which are so remarkable a feature in certain Indian deposits, and 

 which almost invariably limit the principal Indian coal-fields, on one 

 side at least, have been by myself and several of my fellow- surveyors 

 attributed to faulting — a view which Mr. Medlicott disputes. Unless 

 I am greatly mistaken, this character is also considered essential by 

 Professor Eamsay and the officers of the Geological Survey of Great 

 Britain. 



Unquestionably Mr. Medlicott's warning against carelessness in 

 assuming all abrupt boundaries to be faults, merely because there is 

 evidence of crushing, is just ; and I believe that many instances have 

 occurred, where the boundaries in question are obscure, and their 

 length and the apparent throw inconsiderable, in which mistakes 

 have been made ; but these mistakes will, I believe, usually be found 

 to be of small practical or scientific importance. It is not at all my 

 intention to enter into the question of the great lines of abrupt 

 boundary on the flanks of the Alps and Himalayas. Mr. Medlicott's 

 evidence is, in the latter case, for a portion at least of the boundaries, 

 incontestable. But I object to his illustration from the Garo hills. 

 Because he in one spot found a natural boundary, it does not seem to 

 me a logical inference that there is no fault at all. He admits there 

 has been great and abrupt " relative movement." It should not be 

 forgotten that observations at the base of the Garo hills are made in 

 pathless jungle-forest, of a kind of which European geologists can 

 have but a faint conception — where an elephant may be standing 

 within two yards, and yet be utterly invisible — in the densest of under- 

 wood beneath thick high trees, where, as a rule, rocks are only to be 

 seen in stream sections. In such ground, especially, the presence or 

 absence of a "master-fault" would, to my mind, be entirely de- 

 pendent on the form of the boundary, straight or curved ; and if the 



