252 



DOMAIN III. ARGILLACEOUS. 



Kirwan's 

 account. 



Primitive. 



they present a mass of information, compiled 

 with great labour from German authors little 

 known in this country, he has distinguished 

 them, by the divisions of his work, into primi- 

 tive and secondary rocks. His account of the 

 primitive clay slate is as follows: 



" It forms whole mountains, Voigt Prack. 38. 

 But more commonly only partially enters into 

 them, as in Saxony, Charp. 175. Or entire 

 strata, as at Zillerthal, in Tyrol. Its mountains 

 are of gentle ascent. 



" There is no doubt of its being often primi- 

 tive, for in Saxony it frequently alternates with 

 gneiss and schistose mica. 3 Helvet. Mag. 190. 

 1 Berg. Jour. 1792. 536. And with primitive 

 lime-stone. 8 Sauss. 144. And in Hanover gra- 

 nular lime-stone is found betwixt its layers. 

 1 Berg. Jour. 1791. 306. We have also seen 

 that both granite and gneiss often rest upon it. 

 Both Karsten, 3 Helvet. Mag. and Monnet, in 

 25 Roz. 85. sufficiently establish this distinction. 

 There are two sorts of it particularly to be 

 attended to, the harder and the sefter ; the 

 harder border upon, and often pass into, sili- 

 ceous schistus, or basanite, or hornblende slate. 

 The softer border upon, or pass into, trap, or 

 wacken, or rubble stone, or rubble slate, or co- 

 ticular slate, or indurated clay, and the harder 



