48 DOMAIN VIII. DIAMICTONIC. 



considerable part of the combination ; but the 

 rock still preserves the slaty appearance. 



NOME XIL SLATE, WITH MAGNESIA. 



[VALENTINITE, from Basil Valentine (his real 

 name see Dufresnoy, i. 229)5 A. D. 1410.] 



This substance is commonly to be distin- 

 guished by its unctuous or silky appearance. 

 The magnesia sometimes assumes the form of 

 small scales, as at Holyhead, where it is also 

 sometimes invested with a crust of foliated steat- 

 ite, and sometimes includes masses of pure talc 

 and amianthus*. The same interesting spot 

 likewise presents schistose siderite, penetrated 

 with talc or micarel. It has commonly layers 

 of quartz between the plates of siderite. 



HYPONOME I. 



Level. 



HYPONOME II. 



Undulated. 



* Kirwan i. 382. 



