52 T. 31. Meade — Origin of formal Faults. 



It has been shown by myself * and by Davison, Darwin and 

 Fisher, that the secular cooling of the earth cannot, on the most 

 favorable assumptions, bring the outer shell of the globe into 

 compression below a depth variously estimated at from two to 

 five miles, the compression being greatest at the surface and 

 diminishing to zero within these figures of depth or to what 

 has been termed the "level of no strain." The introduction 

 of a molten zone between a thin upper crust and a solid 

 nucleus will not help matters in any way. 



Normal faults, as the name implies, are not confined to the 

 Basin region ; they are world wide. They frequently occur in 

 extensive areas where there are no volcanic rocks, dikes, 

 sheets, ash beds or other signs of "relief of tension by out- 

 pouring of lava or by escape of stream." As associated with 

 strata of mountain ranges, they are more frequent in the sur- 

 rounding plains than in the folded portions exhibiting signs of 

 great compression. 



The theory of normal faulting favored by Professor LeConte 

 is inapplicable outside of the Basin region, and local explana- 

 tions not in harmony with general phenomena are to be sus- 

 pected. 



In my view, normal faulting is not the result of tension 

 through intumescent upheaval, but of decrease of bulk of the 

 underlying matter of the crust itself. This decrease may 

 result from the cooling and consolidation of injected igneous 

 sheets, or from the cooling of portions of the solid heated 

 matter of the crust, or from both combined. In whatever way 

 a diminution of bulk occurs, the overlying strata will by 

 gravity follow up the shrinkage and preserve the solidity of 

 the crust. 



This, I have attempted to show, must, through mechanical 

 necessity, take place by shearing and wedging up of the 

 sheared blocks. It has frequently been observed by geologists 

 that in faulted regions the strata seem as if they had been 

 drawn apart, and that if replaced in their original positions 

 they would not fill the void. Contraction of the strata ex- 

 plains this fact, but tension by arching does not. 



It would take up too much of the space of this Journal to 

 go into further details ; but any one who may desire to pursue 

 the subject, will find the theory fully set out in Chapter VIII 

 of the Origin of Mountain Kanges, and further discussed in my 

 paper on slickensides and normal faults in the Proceedings of 

 the Liverpool Geological Society 1888-9 ; also in a series of 

 articles entitled Theories of Mountain Formation in " He- 

 search " for 1888. 



Park Corners, Blundellsands, in Liverpool, England. 



* Origin of Mountain Ranges, Chap. XI, and various papers in the Philosophical 

 Magazine and Philosophical Transactions by the authors named. 



