SKY. GEOLOGY. GNEISS. 299 



Together with these, which are the most marked and 

 the predominant varieties, micaceous schist of two or 

 three distinct aspects occurs. In general it forms beds 

 of but small extent, the gneiss soon recovering its pre- 

 dominance ; but in one or two places, masses of 100 yards 

 or more in thickness are to be seen. 



The beds of hornblende schist that alternate with the 

 prevailing rock are sometimes simple, at others compound, 

 containing felspar : they are frequently conspicuous for 

 their magnitude. 



Beds of chlorite schist passing into talcaceous schist, 

 or into pale blue argillaceous schist, or into a graywacke, 

 are also found in different places ; and in some cases 

 the mixture or alternation of the former rock with the 

 felspar and quartz that prevail in the gneiss, is such, and 

 the chlorite schist so predominant, that it is difficult to 

 say under which of the two substances it ought in prefer- 

 ence to be ranked. 



A gradual change seems to take place along the eastern 

 coast, from the simplest gneiss, which occurs near Isle 

 Oransa, to the irregular varieties, which predominate at 

 Armadale : while, as we proceed further to the south- 

 west, the schistose ingredient increases nearly to the 

 exclusion of the others. The last stage of the transition 

 from gneiss to chlorite schist is effected by a rock as yet 

 without a name ; a compound of chlorite schist and felspar. 

 There are two varieties of this ; a laminar one, in which 

 the two substances alternate and the external characters 

 of gneiss are maintained; and another, in which the 

 irregular laminae of the schist are intermixed with arena- 

 ceous grains of felspar, so that the usual characters of 

 gneiss disappear. 



Other anomalous substances, which it is necessary to 

 mention, are found in connexion with these rocks. One 

 of these consists of a white felspar traversed by long 

 prismatic needles of hornblende, and it occurs in a separate 

 bed near Loch Oransa. In another, actinolite enters into 



