1318.3 * ON THE FORMATION OF ROCKS. 299 



tides aggregated; of this kind is the graywacke of the 

 Hartz in Saxony^ and generally that species of gray- 

 wacke which alternates with graywacke shist. 



The second is an aggregate with a small-grained, 

 rather crystalline^ cement of a greenish colour, resem- 

 bling a little some kinds of chlorite, which cement 

 forms a great proportion of the rock, as in the range 

 north of Vigo, and Bleyburg in Tyrol. 



The other is an aggregate of rounded quartz, seldom 

 exceeding the size of a walnut, in a shistoze cement, 

 inclining to be fibrous, the cement forming the princi- 

 pal mass of the rock ; as the rock generally found on 

 the borders of the primitive, the first aggregate in the 

 transition formation on the west side of the primitive 

 ridge in North America, in which the quartz is gene- 

 rally of a light blue colour. I found in the valley of 

 Durasa, south of Mount Rose, a rock of the same na- 

 ture. 



S3. Graywacke sMst, an aggregate of small par- 

 ticles of rocks rounded by attrition, united by a ce- 

 ment more or less shistoze, having remains of organic 

 matter, (though rarely) found in it ; and being conse- 

 quently of Neptunian origin. 



This formation, though often accompanying the gi^ay- 

 wacke, yet is much more general and extensive ; it co- 

 vers the north side of the Carpathian and Bohemian 

 chain of mountains, as well as the Tyi^olean and Switz 

 Alps ; increasing in force as it proceeds south along 

 the mountains in Dauphiny ; it probably covers the 

 whole cliain after you pass Mount Cenis, and consti- 



