150 Transactions of the Canadian Institute. [V^oL. VII. 



Black River times" ('92, no). So far as indicated in the context, 

 the only evidence upon which this deduction is founded, is the occur- 

 ence of the Hmestone strata " at a high angle," dipping outward from 

 the central dome of gneiss. The evidence, as stated, seems inadequate 

 to admit of the broad conclusion reached. 



If the ridges were elevated subsequently to the deposition of the 

 strata, i.e., were ridges of deformation, certain necessary results would 

 follow. Over large areas the gneissic structure is frequently parallel. 

 If, in such an area, a ridge is form.ed b\' elevation without faulting, in a 



region where the dips are not ex- 

 actly vertical, the inclination on 

 the side of the new ridge towards 

 which the structure hades would 

 be steepened, and that on the 



Figure s.-If AB represent the position of the side OppOsitC IcSSCUed. A travei'SC 



surface of the gneiss before upheaval, and A^^^^ ^^^^^^ ^^^ ^.j^ j^^ ^j^^ dirCCtioU 



the position of the surface or the dome atter up- -^ 



heaval, then that portion that moves upward at a of hadc WOuld shoW a dcCrease tO 

 will have a less distance to rise than that at /;. . . 



Therefore the dips between « and A will be steepened. a minimum WherC the grade WaS 



Similarly, on the opposite side the dips will be crrgatest, followed bv au iiicreasc 



lessened. Beneath the crest the uplift will be uni- 

 form, and hence there will be no alteration of dip. tlirOUgll the UOrmal at the CrCSt, 

 Where the g-rade <>f the new ridge is steepest the , . 1,1 1 



change from the original dip will be greatest. ^o a maximum where the grade 



was at a maximum upon the op- 

 posite side, and then decrease to the normal (figure 5). In a series of 

 such ridges this divej'sity of dip would occur iiniforjidy across the ridges. 



Secondly, strata adjacent to all the ridges would be inclined in 

 sympathy with the elevation, the greatest inclination being nearest the 

 steepest and highest ridges ; where the inclination of the ridge is very 

 steep the strata would be affected for a longer distance away from the 

 centre of elevation, or if the uplift did not affect the strata at any great 

 distance, faulting and slipping would occur. 



If the uplift took place gradually, or rapidly, during the period of 

 deposition of the strata, the Jiniforin diversity of dip in the structure of 

 the ridges would be as in the first case. The strata would tend to thin 

 out over the crest, if the material were somewhat coarse. If the uplift 

 were very great some of the beds might even end in wedges against the 

 sides of the ridge. The other necessaiy results would be as in the 

 former case, though faulting and slipping are less likely to occur, owing 

 to the softness of the beds. In the sections as usually exposed it would 

 be very difficult to distinguish between intersedimentary and post- 

 sedimentary uplift. 



