522 



DR. C. CALLAWAY ON THE ALLEGED CONVERSION" OE 



facts furnished by the Lettershinna sections greatly attenuate the 

 difficulty. If I am right in my reading of those sections, it is clear 

 that the granite has intruded between the strips of diorite and 

 pushed them apart, without materially disturbing their parallelism. 



But if we reflect upon the probable conditions under which the 

 granite was intruded, even the original difficulty will not appear so 

 great. The displacing power of an intruding current of molten 

 matter will be in proportion to the rapidity of its motion. Dykes 

 of greenstone intruded into faults often contain numerous pieces of 

 fractured rock lying pellmell. But an igneous rock forced along 

 lines of least resistance by tangential pressure may be expected to 

 move with extreme slowness, so that the currents might act rather 

 in the manner of slowly moving wedges than with the irregularity 

 of an ordinary flow. 



Another consideration appears to me of still greater weight. The 

 region under discussion has been subjected to great pressure. If, 

 then, a number of flattened pieces of schist were scattered pellmell 

 through the plastic mass of granite, the compressing force would 

 move the fragments into planes lying at right angles to its own 

 direction. We are familiar with a similar result in the formation 

 of slates, and we may safely infer that the process would be 

 facilitated by the plasticity of the granite. 



3. The Foliation oe the Igneous Rocxs. 



The Foliation of the Granite. 



The foliated structure is well seen in the district south of Glen- 

 dalough. In one spot, the granite runs into the diorite in long 

 tongues striking east and west, that is, in coincidence with the 

 strike of the schists in this area, and here the foliation of the 

 granite is also east and west, and is strongly marked. But where 

 the veins were oblique to the strike of the region, the foliation was 

 oblique and obscure. In another place, where the veins ran north 

 and south, they were intensely contorted. These facts point clearly 

 to the influence of an earth-thrust acting along a north and south 

 line. 



Foliation in the Diorite. 



I noticed this on Xnockseefin, in veins intrusive in schist. The 

 foliated structure is parallel to the longer axes of the transverse 

 sections of the veins and to the strike of the schists. It is 

 obviously due to pressure. Prof. Bonney has examined slides of 

 this squeezed diorite, and he finds no difference between it and 

 hornblende-schist. 



Foliation in Veins of an Acidic Rock. 



Near the summit of Shannarea appear several veins, lenticular in 

 plan, which are not easy to explain. They consist of quartz, with 

 a little mica, probably biotite, and a fair number of garnets. The 

 foliation is very distinct, and coincides with the foliation of the 



