256 ON THE FORM^VTiON OF ROCKS. [My, 



mncli softer and less adhesive. The red sandstone has 

 110 veins of calcspav crossing the stratiiicationj whereas 

 the graywacke shist is generally full of little veins or 

 threads of calcspar, crossing the strata in all directions^ 

 and alternates with beds of compact, small-grained 

 limestone, full of the same veins of calcspar; tlie 

 red sandstone has no such limestone; but a thin stra- 

 tum of a liind of argillaceous limestone or indurated 

 marie, occasionally divides tlie strata of sandstone; the 

 graywacke shist runs into, and alternates with, clay 

 ^late, and roofing slate^ and goes by a gradual transi- 

 tion into the primitive slate and hornblende rocks, but 

 the red sandstone has no clay or rooiing slate in or near 

 it, and generally lies upon the primitive, without any 

 gradation of transition; it is seldom or never found near 

 the graywacke, nor often on the same side of the range 

 of mountains, though when there is no graywacke, or 

 o>.her transition rocks, it occupies their place, and covers 

 immediately the primitive. 



The gypsum found in the red sandstone is in thin 

 strata, ^tiltemating with much tlayinasoft state; the 

 slratuin of gypsum in the transition is powerful and 

 extensive, with the little argil it contains generally in 

 iiie ibrm of a shist or slate. 



The above remarks may perhaps be applicable to 

 what is called in France the Gres de Houillier, a sand- 

 3U)ne of the coal formation, which in Flanders, and o- 

 ther coal ccuntiies, has some appearance of gray- 

 wacke shist, aiid has been taken for such by many min- 

 eralogists. This Gres de Hoiiillier is generally com- 

 posed of sand, with small plates of mica, of a shistozc 

 structure, bat is much softer, and in general the ce- 

 ment not so shistoze, nor does it alternate with any of 



