KiNAHAN — On Granitic and other Ingenite Hocks. 119 



crystals of eyanite ; pyrite may also be detected in it. A specimen of 

 this rock was determined by Mr. D. Forbes to be eklogyte, while ITon. 

 A. Gage says it does not present the physical characteristics of that 

 well-known rock, but properly belongs to the serpentine series. 



Steatyte occurs as subordinate quantities associated with the ophyte, 

 usually at the margin of masses, or in lenticular patches or irregular 

 Teins ; however, in other places it appears in mass. ^Tien fi'eshly 

 broken it is of a pale greenish gi'ey colour, but becomes a pale bluish 

 grey shortly after being exposed to the air ; and subsequently decom- 

 poses into a rusty white or dirty cream-coloured substance. It is more 

 or less fissile, very unctions, tough, splits along the grain, but across it 

 breaks with a hackly fi^acture. 



Steatyte in mass in places graduates into felsityte or homblend- 

 yte. In the countiy north of Killary bay, the previously men- 

 tioned tuffoid portions of the protrusions of felstone (p. 114) graduate 

 through felsityte, and steatitic -felsityte into steatyte, while on Bofin 

 and Sharke islands the steatyte is associated with hornblendyte and 

 talcyte, and the mass formed of these rocks combined appears to come 

 up as a protrusion among the metamorphosed sedim.entaiy rocks, while 

 in the protrusion are peculiar iiTegular pipes, and bomb-shaped masses 

 of compact hornblende rock {Sornhlende-ajjhanyte). (See fig. K, PI. 10.) 



From these circumstances I am led to suggest that the steatyte was 

 originally fine tuff, either basic or felspathic, in which were pipes and 

 iiTCgular veins of igneous rocks, the remains of an accumulation 

 formed in the vicinity of a subaqueous plutonic outburst, similar 

 to that previously mentioned when describing the homblendytes 

 (p. 116). These masses would seem not to have been intruded up 

 among the sedimentary rocks, but rather to have been protrusions, that 

 subsequently were in part denuded away, while round them the 

 sedimentary rocks were being deposited, till eventually the latter 

 enveloped them.^ 



* In favour of this suggestion it sliould be stated that, in the places where horn- 

 blende rock, in combination ^vith hornblendyte and conglomeiitic-schist, form 

 masses that are protrusions in the associated gneiss and schists, the latter rocks 

 seem to be allied to them, having originally been formed of somewhat similar 

 materials. In the neighbourhood of the protrusions of steat\i:e on Bofin and 

 Sharke, the schists are, more or less, homblendic andtalcose, and in the country north 

 of Killary harbour the schists in the neighbourhood of the felspathic mass are, 

 more or less, felspathic, many of them being felsityte. This should be expected if 

 the above is coiTCct ; as part of the accumulation of tuff would remain as an irregu- 

 lar mass, while the portions destroyed by denudation should be deposited around 

 the residue ; and, although not exactly similar, yet, in a great measure, par- 

 taking of its nature. To account for the rocks north of Killary harbour, we 

 might suppose a protrusion of felstone somewhat similar to one of these in 

 Auvergne, except that, instead of being subacial, it was subaqueous ; the outside 

 portion of such a mass would be, more or less, disintegrated, and piilveiised, 

 during the cooHng process, by the water-mass in contact, and thereby produce 

 materials that, when deposited around, woiild fonn rocks very similar in com- 

 position and aspect. 



