The Quartzites of Sauh and Columbia Counties. 131 



zite bed above many of the talcose laminae disappear, while 

 a few of the more prominent curve as they enier it until they 

 take a direction more nearly perpendicular to the laminations 

 of the quartzite. Their behavior with the underlying bed 

 was not observed, it being obscured by a projecting shelf of 

 rock, from the surface of which, however, it was inferred that 

 it was the same, the curvature being probably in the opposite 

 direction. 



That the material forming this schist and the quartzite beds 

 above and below was originally deposited in an essentially 

 horizontal position, does not admit of doubt. That the ma- 

 terial of these talcose laminae was deposited in its present re- 

 markable position and relationship, is not to be supposed. To 

 what then do they owe their origin? 



That the lamination and cleavage of true slate are due to 

 pressure is now considered as demonstrated. That pressure is 

 competent to produce such cleavage and lamination has been 

 verified by direct experiment, with homogeneous as well as 

 heterogeneous material. That some of the so-called schists 

 owe their structure to a similar cause, has been conceded by 

 high authority. Mr. Sorby has shown* that cleavage may 

 even be produced in sandy layers included in slaty material, 

 by the pressure which gave rise to the slate. Bearing these 

 facts in mind, let us go back to a time previous to the meta- 

 morphism of these rocks. The quartzites were then sand- 

 stones and the schist would have been classed as the same with 

 magnesian impurities. The metamorphism of these implies 

 either heat or pressure, or both. But there are no evidences 

 of any source of heat, unconnected with pressure to be found 

 in the region. There are no volcanic or trappean rocks, no 

 deposits of thermal springs. Any source of heat of this char- 

 acter must have been considerable, and should have left its 

 traces, for the area includes more than 150 square miles, about 

 75 of which are occupied by the quartzite ridges. 



*0n the Origin of Slaty Cleavage, by n. C. Sorby, Edinburg. New Phil. Jour., 1853, 

 vol. iv. p. 137. 



