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118 - | GEOGNOSY. — [Boox IL 
2. Schistose or Foliated. : 
The Crystalline Schists form a remarkably well-defined series 
of rocks. Their structure is crystalline, but is distinguished from that 
of the massive rocks by the possession of an arrangement into more 
or less closely parallel layers or folia, consisting of materials which 
have assumed a crystalline character along these layers. ‘The folia © 
may be composed of only one mineral, but usually consist of two or 
more, which occur either in distinct, often alternate, laminz or 
intermingled in the same layer. In some respects this structure 

Fic, 17.—PRoriLe orf A PIECE OF GNEISS, SHOWING THE LENTICULAR CHARACTER 
OF ITs FOLIA, NATURAL SIZE. 
resembles that of the stratified rocks, but is differentiated (1) by 
a prevalent striking want of continuity in the folia which, as a 
rule, are conspicuously lenticular, thickening out and then dying 
away, and reappearing after an interval on the same or a different 
plane (lig. 17); (2) by a peculiar and very characteristic welding 
of the folia into each other, the crystalline particles of one layer 
being so intermingled with those of the layers above and below it that 
the whole coheres as a tough not easily fissile mass ; (8) by a frequent: 
remarkable and eminently distinctive puckering or crumpling of the 
