534 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



probably not a small dyke or injection into a fissure. If it 

 were so, the fissure must have been formed in some most 

 unusual manner. The tabular crystals of albite can be 

 clearly seen, and some black crystals of augite. Some dull 

 patches are crystals of secondary dolomite showing curved 

 faces and absence of lamellar twinning under the micro- 

 scope. In this, as also in the fine-grained aplite, the 

 tabular felspar crystals lie in all directions, there being no 

 trace of fluxional parallelism. 



There remains one feature worthy of close attention. 

 The fine-grained aplite appears to be associated with the 

 medium or coarse-grained aplite in two ways ; it often 

 occurs in blobs or rounded masses which look as if they had 

 been suspended in the coarser aplite, but also occurs as a 

 definite band or "selvage" on either side of the coarser 

 aplites, i.e., between the coarse aplite and the pegmatite* 

 The following section measured from the upper vein near 

 the south end of the quarry illustrates this : — 



Thickness. 



Pegmatite 6 inches 



Pine aplite ... \\ to 2 

 Medium to'coarse aplite 10 



Fine aplite \\ 



Pegmatite ... 12 



Total ... 31 



19. Fetrological description of the Pegmatites and 



Aplites. 



The aplites and pegmatites differ little from point to point 

 except as regards grainsize. It appears unnecessary there- 

 fore, to describe a number of individual specimens, and we 

 give a generalized description, first of the pegmatites and 

 then of the aplites, in tabular form. 



Pegmatites. 

 Megascopic Description. — Colour : At a distance, dark 

 greenish-grey ; near at hand, speckled white, dark green 



