I5Y THE REV. J. MILNE CUUKAN. 209 



striking in every direction through the clear quartz. A power of 

 one hundred diameters shows them in great abundance. They 

 branch, Bometiraes meet at a point, fifteen or twenty diverge Prow 

 one point, and sometimes opaque blebs are found at various 

 points along their length, <>r, more often, at the end. I can offer 

 no explanation as to their real nature. Cavities are abundant in 

 the quartz. They can be detected in every slice. I have noticed 

 one spontaneously moving bubble. Besides the trichites and 

 bubbles, tubes oan be seen in the silica with a power of fifty 

 diameters, They are evidently tracks left in the plastic; mass by 

 moving bubbles of gas. 



Examined in polarized light, with crossed Nicols, the quart/ 

 displays the usual gorgeous bioad sheets and bands of colour, one 

 colour imperceptibly shading into another. In very thin slices 

 it appears a dull blue-grey. The great abundance of cavities in 

 the silica of all the slices is explained by (he fact that the quartz 

 was the last mineral to crystallize. When rocks that have cooled 

 from an igneous magma are studied, it is often noted, as we should 

 expect, that the most fusible mineral was the last to crystallize. 

 But it is found that this does not apply to granitic rocks. Every 

 student, knows that quart/, is commonly called infusible, while the 

 felspars are considered fusible in various degrees. In the con- 

 solidation of granite from an igneous fluid or paste, felspar was 

 the first to crystallize;, while tin? more infusible quartz filled up 

 the interspaces and was the last to solidify. Our granite is no 

 exception to the rule, for the silica occurs in an amorphous stale, 

 enclosing tin; other minerals as in all true granites. This is 

 explained by supposing that the original plasticity was induced in 



some other way than by what- we understand as Avy igneous 



fusion. The fluid inclusions prove the presence of water and 



various salts. Tin; quartz, being the last to harden, took in any 



fluid residue and, from its enduring nature, retained it. A notable 



feature of the quartzes, under the microscope, is the presence of 

 microscopi<- dust, which seems to have accumulated on the out ide 

 surfaces of the quartz granules. 



