ElylSHA MlTCHELIy SCIENTIFIC SOCIETY. 62 



structural effects are due to dynamo-metamorphic action 

 on materials of different composition. The argillaceous 

 types might more properly be called the slates (clay- 

 slate, thon-schiefer, argyllite, phyllite) as the}^ contain 

 more uncrystalline matter, and possess a more definitely 

 slaty structure. So also bedding planes are more easily 

 distinguishable in these, if at all; and altogether their 

 sedimentarj^ or clastic origin is more evident. At the 

 same time they are metamorphosed in varying degrees, 

 and possess many secondary cleavage structures. These 

 slates often have a calcareous tendency in their composi- 

 tion, as is exemplified by the numerous small calcite seams 

 that intersect them, and the coatings of calcite on their 

 cleavage planes. 



The term talc {talcose, talcoid) slate or schist, used by 

 Emmons and Kerr, and generally by many others, is a 

 mistaken one. It is true that it is perhaps an excusable 

 error, for these slates and schists are often so soft and 

 greasy that the resemblance to talc is very great. How- 

 ever, chemical analysis and other characteristics would 

 place the mineral in the class of hydro-muscovite or seri- 

 cite, the percentage of magnesia being far too small for 

 talc. Several analyses of type specimens of this rock 

 from the Haile gold mine in Lancaster county, S. C, by 

 Dr. Chas. Baskerville, of the University of North Caro- 

 lina, show: 



SiO, 44.61 61.02 



AlA 31.57 25.54 



FeO 3.55 4.46 



CaO 0.20 0.60 



MgO 0.22 0.14 



MnO 0.16 



Na,0 6.96 



Kfi 6.97 



H3O 5.80 



100.04 

 The term that I shall therefore use as more appropri- 



