344 S. B. Medlicott — On Faults in Strata. 



spread and deep-seated forces are altogether dominant. It is, indeed, 

 an open question to what extent such is, or has been, in remote times, 

 the case : and, therefore, one should look out for any marked coinci- 

 dences in direction, being careful at the same time to remember that 

 denudation and redeposition are apt to follow ancient main lines of 

 flexure. But it is also evident that faults may be determined by cir- 

 cumstances that would put general symmetry of direction out of the 

 question, — by differences in thickness, in texture, in position with 

 reference to more resisting masses, of the strata acted upon. There 

 are, besides, the manifold marks of origin of the movement, whether 

 from simple compression, or compression with subsidence, or with 

 elevation. Amid such complexity of causes, active and passive, it 

 is manifestly Procrustean to force the faults of a district indiscrimi- 

 nately into unmeaning " systems," as is sometimes done, to the neg- 

 lect and confounding of more direct and importarit conclusions. 



Two examples will illustrate part of what has been set forth. In 

 north-east Bengal, sandstones of the Cretaceous period are found 

 rolling up to the south base of the G-aro Hills, where they are at 

 last seen dipping at very high angles (over 80°) from, and in imme- 

 diate proximity to, the gneiss that forms the high plateau — a mode 

 of relation highly suggestive, some would presume, of a fault. In 

 this case, moreover, the required indirect evidence is partially, indeed 

 I may say fully, present ; at some few miles distance, at an elevation 

 of 4,000 feet on the plateau. Cretaceous sandstone of the same horizon 

 rests undisturbed : there being no doubt of the two having been 

 originally continuous. Great, and more or less abrupt, relative 

 movement must be accounted for. A reference to the direct evidence 

 fully satisfied me that there was no master-fault : by hunting up 

 the boundary an actual contact was found showing the plane of 

 junction with the gneiss to coincide with the dip of the sandstones, 

 and the bottom bed of the latter to be conglomeritic, containing large 

 waterworn debris of the gneiss. There was no sign whatever of 

 friction or of local crushing. It was evident that the existing ar- 

 rangement had been effected by some mode of flexure or of yielding, 

 vsdthin the mountain mass, whereby the Cretaceous surface of deposi- 

 tion had been brought near to the vertical. It is difficult to suppose 

 such an amount of movement taking place within a mass of rocks 

 without some fissuring and sliding (faulting) ; but hardly any 

 amount of such secondary effects would, to my mind, justify the 

 representing such a feature as a fault-boundary. It may be well to 

 add that the mistake I now combat has not been made ; I believe 

 I am the only geologist who has seen this Garo Hill section. 



Again, in the low jungly hills at the base of the north-west 

 Himalaya, there is a very continuous and well-marked boundary 

 between two groups of the sub-Himalayan series. The younger 

 deposits very generally dip towards the older at high or low angles, 

 apparently going into or under them ; both are very partially indu- 

 rated, and the confusion and crushing near the contact is consider- 

 able. Here, again, one might suppose a plain case of faulting. It 

 is true there is no certainty that the younger strata had ever stretched 



