3'70 Scientific Proceedings, Royal Dublin Society. 



Polariscope. — With crossed nicols the alternating bands of tre- 

 molite (?) and serpentine are clearly defined ; the former showing 

 the fibrous structure, and colours of yellow passing into purple ; 

 the latter, varying shades of indigo blue. 



No. 4. Banded dark and light sap-green rock, with small flakes 

 of mica in the folia. 



Microscope. — Surface showing net-like spaces of light-yellow 

 serpentine, mixed with clear colourless spaces, through which are 

 distributed black strings of magnetite dust, sometimes intruding 

 amongst the narrow meshes of the net- work, at other times 

 forming long, slightly-bent bands, with jagged and branching 

 sides. Tremolite is absent from this specimen. 



With a high power (one-fifth objective and No. 2 eye-piece) the 

 strings are seen to consist of magnetite dust, or very minute 

 grains, which have apparently been extruded from the clear or 

 coloured spaces during the process of metamorphism, and are 

 now difiused through the minute cracks, and fissures, and join- 

 ings of the individual grains of serpentinous matter. 



Polariscope. — The polarization in this case differs from that of 

 the former specimens. With crossed nicols the serpentinous 

 mineral often shows a wavy-banded structure of varying shades 

 of indigo blue, like some varieties of agate. Throughout this 

 mass are strings and branching veins of a mineral, evidently of 

 newer formation, and polarizing with an opalescent play of 

 colours where the prisms are crossed. I am uncertain as to its 

 nature, but it may possibly be quartz. 



