O74 Scientific Proceedings, Royal Dublin Society. 
Tn conclusion, a banded and perfectly crystalline gneiss appears 
on the foregoing evidence to be capable of being produced solely 
by “mass-dynamic” agencies, acting on anon-homogeneous rock, 
as one type of which we may regard the porphyritic andesite 
described in the present paper. 
EXPLANATION OF PLATES. 
PLATE XXVI. 
Ie ; 
1.—Weathered surface (54 x 42 cms. approx.),! of the porphyritic 
andesite at Deerpark (8), showing irregular arrangement of 
the felspar phenocrysts in the right-hand top corner. Part of 
the rock is slightly sheared. 
_ 29.—Surface of rock (67 x 52 cms.) approx.) near the last, showing 
first signs of alteration by pressure in the general parallelism 
of the felspar crystals, A quartz vein, sheared by the same 
movement, is shown in the upper portion of the photograph. 
PLATE XXVII. 
Fie. 
1.—Photo. of hand-specimen (18 x 8 ems.), showing glomero-por- 
phyritic arrangement of the felspar siystnals on weathered 
surface. 
2.—Photo. of hand-specimen (8 x 4 cms.), showing flattened cross- 
sections of the felspars in an intermediate stage of elongation. 
3.—Photo. of hand-specimen (11 x 7 ems.), showing appearance of the 
felspars in a direction parallel to that of elongation, and almost 
in the final stage of alteration. 
4.—Photo. of part of hand-specimen (15 x 5 cms.), showing banded 
character of the schist produced by the effects of pressure 
and re-crystallization from the porphyritic andesite (fig. 1). 
1 The dimensions given in brackets are those of the original specimens, or 
portions of specimens, shown in the photographs. 
