H. B. Medlicott—On Faults in Strata. 473 



IV. — On Faults in Strata. 



By Henry B. Medlicott, B.A., Geological Survey of India. 



("With a Diagkam.) 



SINCE I first saw my short notice on *' Faults in Strata " in print 

 (Geological Magazine, 1869, Vol. VI., p. 341), I have been 

 anxious to remove a blemish of apparent flippancy in alluding to 

 systems as applied to faults. I had indeed in view cases where that 

 method had been used imitatively — with the tacit assumj)tion of an 

 established and well-understood meaning; but I lost sight of the 

 fact that serious special work had been devoted to the subject, and 

 my remark was unqualified. I have to thank my friend Mr. W. T. 

 Blanford for an opportunity of making this correction, as well as of 

 adding some further considerations on so important a point in the 

 principles of stratigraphy. 



In his short answer to my paper (Geol. Mag., 1870, Vol. 

 VII., p. 115), although Mr. Blanford says he difiers from me in 

 opinion, it is very gratifying to me to find that there is far more 

 agreement than disagreement between us upon the fundamental 

 points at issue. Firstly, Mr. Blanford seems to grant that dips are 

 unreliable as proofs of faulting. This admission might have 

 removed the surprise expressed that my objections had not been 

 answered, for all the special instances I impugned were of this 

 nature. No one can doubt that faulting is attended by more or less 

 bending of the strata, and such as, if strictly analyzable, would give 

 a correct account of the mechanical action ; but it can no longer be 

 matter of opinion that dips of every form and degree are produced 

 at the contact of rocks without any attendant faulting ; and there is 

 no mode of discriminating the causes in the effects. In this diffi- 

 culty the importance of the direct evidence of the contact is not, I 

 venture to maintain, to be underrated. Mr. Blanford's limitation of 

 possible error from this source to small and unimportant cases is 

 based upon the independent evidence (of straightness) which he 

 conceives always to attend great faulting; on any other grounds this 

 restriction could not be made, for the simulation of disturbance takes 

 place on every scale, as, for instance, in the examples I brought 

 forward from the Sub-Himalaya and the Garo Hills, where the 

 throw, on the supposition of faulting, would amount to many hun- 

 dreds, or even thousands, of feet. 



On another most important point, that of the direct evidence, Mr. 

 Blanford gives me all the satisfaction I could have expected. He 

 says, indeed, that he has not, as a rule, noticed signs of friction in 

 sections of undoubted faults in mines or cliffs ; but it is not stated 

 that he had looked for them ; and as he now only endeavours to 

 show cause for the removal of such marks, it may perhaps be inferred 

 that there is a presumption of their having been always to some 

 extent produced originally. That this evidence varies greatly in 

 degree is certain : thus, Mr. Mammat in his " Geological facts to 

 elucidate the Ashby Coal-field," in describing the characters of faults, 

 says, "The two sides of the fault are generally so crushed in slipping 



