222 C. CALLAWAY ON THE GRANITIC AND 



I. The Geanite. 

 1. State oe peeviotjs Opinion. 



Mr. E. H. Scott, P.K.S.*, claims a metamorphic origin for tMs 

 rock. 



Mr. E. H. Blake f takes the same view. 



In a subsequent paper J Mr. Scott offers a theory of the origin 

 of the granite. He considers that all the rocks of the region were 

 originally stratified, but that, by subsequent metamorphism, some 

 of the beds were altered into granite, some into gneiss, and some 

 into other kinds of rocks, without much altering the relative posi- 

 tions of the strata. 



The Eev. Dr. JSaughton, F.R.S.§, regarded the granites as " being 

 stratified and not intrusive, and therefore varying considerably in 

 different localities according to the beds from which they have been 

 formed by the metamorphic action." 



Professor Hull || accepts the metamorphic theory of the granite, 

 but regards it as of " Laurentian " age; and the schists which follow 

 it on the east and west are referred by him to the "Lower Silurian," 

 the structure of the district being, in his view, on the type of the 

 Highlands of the north-west of Scotland, This writer agrees with 

 previous observers that the granite " contains beds of crystalline 

 Hmestone/' and that it is " foKated and bedded ; " and he adds that 

 " the upper beds which occur along the south-eastern margin are 

 largely interstratified with hornblendic and micaceous schists." 



2. The Geanite Peomontoet. 



The granite appears in several patches in Donegal. The chief 

 area is a squarish mass sending off from its north-eastern corner an 

 arm or promontorj^, about fourteen miles in length, and in breadth 

 tapering from six miles to three. The arm strikes nearly north- 

 east. Disappearing under the schist near Glen, the granite reap- 

 pears in Dunaft' Head, and again in Malin Head. These outlying 

 patches are precisely on the north-easterly prolongation of the strike 

 of the promontory. There is distinct foliation in the promontory ; 

 but I am not aware of anj' in the main mass or in the outlying 

 patches to the north-east. This promontory will therefore receive 

 our chief attention. 



3. Eelations between the Geanite and the adjacent Schists. 



The evidence for the sedimentary origin of the granite adduced 

 by Prof. Hull, agreeing, as it did, with the observations of previous 

 observers, left me in little doubt that I should find the old gneiss in 



* Journ. Geol. Soc. Dubl. vol. ix. p. 285. t Ibid. p. 295. 



X Eeport Brit. Assoc. 1861. 



I Quoted in the ' Memoirs of the Geological Survey of Ireland ' (105 and 114, 

 p. 9). 



II Trans. Roy. Dubl. Soc. ser. 2, vol. i. (1882). 



