THE CONWAY SCHISTS. 



197 



description of a vein of hard, vitreous quartz 7 inches in width, which runs 

 across the face of the hmestone; it is represented in fig. 12, p. 198. 



The large vein is twisted and the limestone is kneaded into the com- 

 pact quartz and drawn out into long filaments can-ied down into the center 

 of the vein and j^inched off" in it, and the smaller veins are contorted still 

 more remarkably. The limestone 

 has received a marked fluidal 

 structure in the apophyses, which 

 penetrate the quartz throughout 

 its whole mass in curving bands, 

 which fit themselves with more or 

 less success to the complex sui-face 

 of the vein. Under the micro- 

 scope the limestone shows all 

 stages in the development of a 

 cleavage by slipping caused by the 

 pressure (Ausweichungsclivage of 

 Heim.') . Portions of a thin section 

 cut at right angles to the cleavage 

 plane break up into a series of very 

 long, thin wedges, placed with tlieir 

 cutting edges pointing alternately 

 in opposite directions. Each wedge 



shows a fluidal structure, expressed rm. n.— Map showing the protrusion of the limestone of the 

 _ ^^ ^, />1T n 1 Conway schist through the Leyden argillite. Whately. 



by the bendmg ot the hues oi coal 



particles toward its head. This slipping of the wedges alternately to right 

 and left concentrates the coaly particles somewhat along the boundaries of 

 the wedges, by which they themselves become more distinctly defined, and 

 at last confluent into a new plane, marked at once by a cleavage and a 

 color banding. 



CONTACT METAMORPHISM OF THE LIMESTONE BY GRANITITE. AKGENTINE. 



A very interesting exposm-e occurs on the river road from Leeds 

 to Haydenville, near the junction of the biotite-granite (granitite) and 

 the muscovite-granite. The former is very confusedly melted into the 



' Untersuchungen iiber den Mechanismns der Gebirgsbildung, Basel, 1878. 



