The River Port Hutton to Smithford 



For this purpose a thin layer of Canada balsam is 

 spread over the section and a thin cover glass placed 

 above. It is now ready for examination. 



The frontispiece shows the appearance of our section 

 under the microscope, and it is seen to consist of small 

 grains of a dark gray opaque substance (Magnetite) ; 

 some crystals and grains of a pinkish mineral, showing 

 numerous parallel cracks in two sets, which intersect 

 each other at a little less than 90 (Augite), and other 

 crystals which are colourless but slightly cloudy in 

 appearance, and of lath-shaped outline (Plagioclase 

 Felspar). In addition to the above there is a grayish- 

 brown substance which fills up the spaces forming a sort 

 of ground-mass or matrix, and which proves, on optical 

 examination, to be glass, while there is also some olivine. 



Thus we find that the basalt consists of a granular 

 aggregate of Magnetite, Augite, Olivine, and Felspar, 

 with some glass in the spaces between the crystals. 



107 



