'/'. M. Reade —Origin of Ntfrmal Faults. 51 



Aki. X, — Origin of Normal Faults: by T. Mel lard 

 Reade, C.E., F.G.S., etc 



In the October Dumber of this Journal, Professor LeConte 



gives an explanation of the origin of normal faults marked by 

 ins well known lucidity and graphic power. 



The conception is however not a new one, as may be seen on 

 referring t<> Geikie's Text book of Geology (page 315, first ed.), 

 Beete Jukes' Manual of Geology , and a paper by I. M. Wilson 

 and correspondence thereon in the Geological Magazine for 1868. 



A- I happen to have devoted a good deal of time and study 

 to a consideration of the same subject, I may perhaps be 

 allowed a little criticism. In the first place I would point out 

 that Professor LeConte has left out of consideration the expan- 

 sion of the strata above by the heat of the intumescent, mol- 

 ten mass required to produce anticlinal tension and which 

 would completely neutralize such tension excepting at or near 

 the surface. As an illustration, I may point to the fact that 

 normal faulting was not produced by the intumescent masses 

 or laccolites which gave birth to the Henry Mountains. What 



tarred was radial splitting, not parallel faulting and the 

 slipping down or lifting up of several blocks. It may be 

 urged that this is not a parallel case as the basin faults resulted 

 from an intumescence on a much grander scale with less pro- 

 portional arching or doming up. It is demonstrable that the 

 heat of such an enormous molten mass would, by expansion, 

 put the superincumbent strata into compression, excepting near 

 the surface, for the lengthening of the strata by increase of 

 temperature would far exceed the lengthening by arching. 

 Any tension would be confined to the surface layers and the 

 rifting would be radial. 



Again there is another difficulty connected with the " flota- 

 tion theory." It is not yet explained how, if the underlying 

 molten matter is of greater specific gravity than the material 

 of the crust, it can ever well over the surface in sheets of lava. 

 I do not say this objection cannot be surmounted, but it leaves 

 the theory very incomplete until an explanation has been given. 



A complete or satisfactory theory of normal faulting should 

 account for the phenomena all over the world, and not merely 

 in the basin region. I venture to affirm that there is no evi- 

 dence other than the requirements of certain theories of the 

 earth, of such a universal, or nearly universal sheet or zone of 

 molten matter as is assumed by Professor LeConte. It is also 

 reasonable to ask if the crust of the earth be an extremely thin 

 shell, floating upon a sub-crust liquid, whence comes the lateral 

 pressure required for the formation of mountains by folding? 



