1894 THE MICROSCOPE. 165 



up stone after stone would say to himself — *' This is 

 granite from the Central Grampians ; " or, " this again 

 is gneiss from somewhere betw^een the ^N'airn and the 

 Spey, this micaslate with garnets from the head waters 

 of the Nairn," and so on. And just as the geologist may 

 at times be able to refer a rock to a particular and very 

 definite locality , at other times only to some indefinite 

 point of a very wide range of country over which it may 

 be known to exist in situ ; so we, in virtue of these in- 

 clusions, may be able to refer our quartz grains some- 

 times to a very definite locality, sometimes only to an 

 indefinite point of a very wide track indeed. 



Now, it may be stated as broad generalities — to which 

 I do not venture to say there are no exceptions — that 

 regular inclusions are to be found in greatest numbers 

 and in highest perfection in gneiss ; that acicuhar crys- 

 tals have their natural home in granite, and the irregu- 

 lar group also claim the same origin. Examples are 

 shown of regular inclusions from gneiss of Findhorn and 

 of Sloch-na-Muich (figure 3) ; the whole of which are par- 

 alleled by examples of regular inclusions in quartz 

 grains from the whole of the series of the Elgin Sand- 

 stones (figures 4, 5,) they exist in varying proportions — 

 from 14 per cent in Spynie to 48 per cent in the sea sand 

 of Lossiemouth. Unfortunately, however, for our hope 

 of establishing a rigid generalization, the local granites 

 are found to contain regular inclusions in greater num- 

 bers than I can remember to be the case in any granites 

 I have ever examined. This is due to the fact that all, 

 or mostly all, of them have been derived from the gneiss 

 by passing through a higher stage of the same metamor- 

 phic process which originally produced the gneiss itself 

 — in other words, the process that produced the gneiss 

 has gone a step farther and produced granite. There 

 will, therefore, occasionally be some little diflBculty as to 

 the origin of a particular grain on this score; but means 



