DIRECTION OF THE DEFORMING FORCE 337 



Carolina there is a great overthrust fault whose horizontal movement is 

 visibly from 10 to 20 miles. The plane itself can be followed beginning 

 at the west in the Middle Ordovician and passing eastward and down- 

 ward through thousands of feet of Ordovician and Cambrian deep into 

 the Precambrian granites. In places the overthrust mass composed of 

 massive Cambrian quartzites rests on weak Ordovician shales ; in other 

 places massive Precambrian granite, mashed into horizontal layers by 

 shear planes, rests on the edges of vertical Cambrian shales and lime- 

 stones. The weak beds are scarcely even slaty, while the massive granites 

 have been mashed and sheared. Having in view the relative behavior of 

 the pliable and the massive beds, which follows a miiversal rule in the 

 Appalachians, it seems impossible that the weak Ordovician shales should 

 have forced themselves downward into regions of greater strain and 

 pushed aside the massive Cambrian quartzites. It is even more incred- 

 ible that the weak Cambrian shales should have thrust aside the massive 

 granite and burrowed beneath it. Even if such an attempt should be 

 made the enormous difference in relative strength of the two rocks would 

 have prohibited any downward motion on the part of the shales. 



An instance of this on a large scale is the great Cumberland thrujst 

 block already alluded to, in which the massive Carboniferous Lee con- 

 glomerate, 1,200 feet thick, has been push'ed far northwestward up and 

 over the shales and sandstones of the Pennsylvanian and Silurian for at 

 least 10 miles. On a still larger scale the excess compression and uplift 

 at each of the three great salients of the Appalachian gives testimony to 

 the same thing. It is not mechanically possible that the shales and sand- 

 stones of the Carboniferous should have underthrust the older, massive 

 sediments and granites and raised masses of them covering thousands 

 of square miles. 



Another line of evidence on this point is the depth of the major syn- 

 clines. If the folds were raised by underthrusting, then the synclines 

 were the active factors while the anticline^ were passive. As already 

 explained, the principal synclines are roughly of the same depth with 

 reference to sealevel. Departures from this, however, are in the opposite 

 direction from what would be expected if the plateau masss were under- 

 thrust against the folded mass. The eastern of the great synclines are 

 higher in relation to sealevel than the western ones, instead of being 

 lower, as the underthrusting theory would require. This general ar- 

 rangement of depths, however, is precisely in accord with the idea of 

 overthrust from the southeast. 



The general distribution of intensities of deformation furnishes strong 

 evidence on the direction of the movcm„r.t. Fold«, faults, and meta- 



