Lesley.] jgg [March. 



ture of the bottom on which they lie probably determines, more than 

 any other determining cause, the amount of disturbance in the 

 normal curves of an uplift. The lateral thrust of horizontal tertiaries 

 over a ragged bed of already upturned secondaries, or of fiat and soft 

 kainozoic strata over an already formed palaeozoic topography, cannot 

 result in symmetrical anticllnals and synclinals; and the amount of 

 hitch and catch below, and therefore of crack and shove above, must be 

 proportional, (1) to the roughnessof the old surface, and (2) to the thin- 

 ness of the new formation. But in the case of the Appalachians, both 

 these proportionals are in the lowest ratio : (1) The palaeozoic mass is 

 seven miles thick, and (2) It lies conformably on the " azoic," if not 

 on the " hypazoic " surfaces, so far as we can see, or with local ex- 

 ceptions ; and there is reason to believe that where this is not the 

 case geologically, it is the case practically ; for the Potsdam sandstone, 

 Quebec group, Taconic system or Primal Formation (whichever 

 name we prefer), probably lies upon an already planed off surface of 

 Laurentian primaries. Hence the wonderful symmetry of the palaeo- 

 zoic vaults and basins, the almost total absence of faults (until one 

 goes far south), and the infre(juency and smallness of earthquakes. 



Hence also the high probability that the anticlinals were unbroken 

 at the crest. A broken anticlinal mvist, in ninety-nine cases in a 

 hundred, develop a fault. In the south, a system of broken anticli- 

 nals have developed a magnificent system of parallel faults. If the 

 symmetry of our northern anticlinals is the first argument against 

 their being originally broken, the absence of faults is a second ; a 

 third is to be found in the many instances of unbroken small anticli- 

 nals, unbroken even when overturned and collapsed ; a fourth is to 

 be found in the absence of any trace of a break in the symmetrical 

 end mountains, formed by the closing of the outcrop walls of an anti- 

 clinal valley at both ends of it; a/i/th is to be found in the side gap 

 structure, which universally accompanies and characterizes the anti- 

 clinal structure ; a sixth is to be found in the total absence of lakes 

 along the anticlinal axis; a seventh is to be found in the evident com- 

 pensation for room lost by room gained along any given cross section. 



At this last point I think lies the solution of the problem. A true 

 section of the crust, transverse to the waved structure, would show a 

 perfect compensation between the sum of the outside and inside 

 curves of the side by side lying anticlinals and synclinals; such a 

 compensation as would distribute the slip between the rock faces, or 

 back-and-belly planes of the stratification, through the whole mass, 

 and thereby reduce it at any given point to a minimum. This dis- 



