J92 LEWIS. GEOLOGY. 



both these a sudden and complete change in the direc- 

 tion of the laminse takes place, the one set abutting against 

 the other without any apparent intermedium. In one the 

 position is at right angles, in the other oblique.* Such 

 an union may be supposed to have taken place at the 

 same period when the other dislocations and contortions 

 were produced, the disjoined parts being capable of re- 

 uniting while in a softened state. 



A fact somewhat similar, perhaps identical, is described 

 by Saussure as having occurred to him on the glacier 

 of Miage. He calls the rock a granitel of schorl and 

 felspar, but offers no conjecture respecting it. Consider- 

 ing the state of mineralogical nomenclature when he wrote, 

 it is not improbable that his granitel was a gneiss resem- 

 bling this. 



I have on different occasions described rocks occurring 

 in the gneiss, of a character distinct from it, such as 

 micaceous schist, talc schist, graywacke, and clay slate. At 

 Loch Carlowa a similar circumstance is seen, the rock, 

 which is of a very peculiar appearance, consisting of dark 

 blue quartz interlaminated with black mica. A more 

 remarkable example of the anomalous varieties of gneiss 

 may be observed towards Oreby on different parts of the 

 shore, where it forms an extensive range of rocks. It 

 consists of an orange red felspar, with a harsh granular 

 fracture proceeding apparently from an intermixture of 

 quartz, containing distinct scales of an argillaceous schist 

 mixed through it in a very regular manner and in a 

 laminar direction. In the same place green compact 

 felspar, similar to that of lona, is found in great abun- 

 dance, forming distinct beds in the gneiss, or dispersed 

 through it in thin plates and prolonged fibres. 



Not far from this place may be seen one of the most 

 interesting varieties which occurred in the course of this 

 investigation. It consists of the most usual intermixture 



* PI. xxxi, fig. 3. 



