RED PRIMARY SANDSTONE. 333 



in two modes. In Sky, the gradation is produced 

 by tiie gradual attenuation of the beds of argilla- 

 ceous schist which so frequently alternate with 

 this sandstone. These gradually become the la- 

 minfe of a variety of gneiss which is described in 

 the account. of that rock ; and, finally changing 

 their character into chlorite schist, they produce 

 another variety which, in a manner equally im- 

 perceptible, passes into the best characterized 

 beds of that substance. In other places, the beds 

 of the argillaceous schist form the bond of union ; 

 alternating in such a manner with the strata of the 

 sandstone, and with those of the gneiss also, that 

 it is impossible to fix on a point where the tran- 

 sition can with certainty be said to take place. 



The transition from the red sandstone to 

 quartz rock, is, on account of the affinity of the 

 two, so easy, that it requires no particular notice ; 

 particularly as it is mentioned in treating of that 

 substance. 



Besides these extensive alternations of the 

 great tracts of red sandstone, the strata alternate 

 with many varieties of argillaceous schist as was 

 noticed in the last paragraph; but most ire- 



