166 THE MICROSCOPE. Nov. 



have been taken to keep the error from this source as 

 small as possible. As a rule, however, grains with reg- 

 ular inclusions are to be referred to the gneiss as their 

 original home. 



The acicular group has proved a very interesting one, 

 for the reason that I have been able to trace most of them 

 to very local and very definite origins (figures 6, 7). The 

 group may be divided into some seven sub-groups, 

 as follows : 



GR4.IXS WITH ACICULAK INCLUSIONS. 



1. Closely packed needles in clear quartz. 



2. Closely packed needles in smoky quartz. 



3. Associated with red or violet or dark hexagons. 



4. Sparsely packed in yellowish quartz. 



5. Associated with clear regular inclusions. 



6. Zig-zag needles. 



7. Very dark closely reticulated ; only two specimens seen. 



You will observe that all of them are granites. I 

 think I have already sufficiently described all the mem- 

 bers of the group, except, perhaps, group 3 (figures 8, 9). 

 It is a very interesting one indeed. Sometimes the hex- 

 agons and needles are mixed up in inextricable confusion. 

 At other times a needle starts out ; it is interrupted ; a 

 few well-formed hexagons succeed at intervals along the 

 same definite line ; then the series is closed by another 

 needle similar to the first, still extending in the same 

 line. Sometimes a needle breaks into a series of very 

 indefinite dots, to merge again into another needle at the 

 other end ; or again, lines of dots take the place of need- 

 les altogether. This is what we see with ordinary pow- 

 ers of the microscope, but, when we pass to higher and 

 higher powers, these indefinite dots are found to resolve 

 themselves into regular hexagons, in all respects similar 

 to the larger. It is the old story of Herschel and the 

 star-depths over again — only here rehearsed at the other 

 pole of infinity. The more he increased the powers of 

 his telescopes, the more and more did the hazy nebulae 



