KiNAHAN — 0)1 Granitic and oUier Itujenite lioclin. 100 



to be in operation. The foliation is linear, parallel, and perpendi- 

 cular, or nearly so, and in general the only original structure 

 that seems to affect it, seemingly, is the strike of the stratification. As 

 the gneiss became more and more granitoid, and perhaps also granitic, 

 the original structure gradually became obliterated, and the foliation 

 more and more perpendicular.'^'* The only other structure that in 

 places seems to resist the change is that of the congiomeritic gneiss. 

 Usually the contained blocks in the latter, as the rock changes from 

 schist to gneiss, become elongated, with the foliation curling more or 

 less regularly round them (fig. P, PL 9) ; and as the rock graduates 

 into granitoid- gneiss a linear parallel foliation is developed, obliterating 

 the congiomeritic foliation, the matrix becoming a more or less fine 

 gneiss, and the contained blocks coarse gneiss, the margins of the 

 latter, as shown in the sketch (fig. D, PL 9), being still traceable ; 

 but eventually one kind merges so completely into the other that, ex- 

 cept on very minute examination, no , difference will be observed. 

 This, however, is not always the case, for, in some places, the enclosed 

 blocks will remain distinct in both composition and aspect ; moreover, 

 these will deflect the foliation in their vicinity, it cui"ling round them. 

 Furthermore, these blocks, although generally more or less elongated, 

 will not always be so modified, as in a few rare instances they were 

 remarked to be more or less angular, the latter even having been 

 observed in the intrusive oligoclasic-granite (see fig. E, PL 9.) In 

 the common gneiss of the gneist series, felspar and felsite, or even only 

 felsite, may be present associated with the mica and quartz ; but in 

 the granitoid-gneiss all the constituents seem to be developed in 

 regular crystalline particles, no felsite matter remaining, it all ha-^dng 

 been developed into quartz and felspar, and hereafter the microscopist 

 may prove that the granitoid-gneiss ought not to be kept in the gneiss- 

 series, but rather included among the granites, and called Foliated or 

 Gneissoid-granite. ISTevertheless the granitoid-gneiss, or the gneissoid- 

 granite, will always be the passage rock between the gneiss and the 

 typical granite. The accompanying section (fig. R, PL 12) shows 

 the passage from the schist into typical granite. 



Metamokphic Deefv-ate Rocks. — Schist. — The most conspicuous 

 rocks of this class that were noted in the area to which this essay 

 refers are : — Argillyte, or Argillous-schist, Micasyte, or Mica-schist, 

 Qua/rt%yte, or QuaHz-schist, Sornblendyte, or Amphihole-schist, Chlorityte, 



generally con?;picnoiisly developed, but sufficient to induce foliation, and similar 

 in their sinuosity and vagaries to those found in the schistose-limestone, schistose- 

 dolomyte, and ophyte. 



* In the Geology and Zoology of Abyssinia, p. 169, Blanford calls special atten- 

 tion to the regular and nearly perpendicular foliation in the gneissic rocks, not only 

 of that country but also of western India. That observer suggests that it is 

 due to cleavage in the original rock. This, however, to me seems improbable, as 

 one and the same cause probably affect both the Irish and the African rocks, and 

 in Ireland it was not cleavage. 



K. I. A. PBGC, SEE. II., VOL. II., SCIEXCE. Q 



