216 EEV. J. MILNE CUREAN. 



Galway Bay, Ireland.* Slices 61 to 69 inclusive, present very 

 much the same characters, the minerals present in them being 

 1. quartz, 2. orthoclase, 3. plagioclase, 4. biotite, 5. hornblende, 

 6. sphene, and 7. muscovite. 



Slice 65. — The granites of Bathurst and Moruya often contain 

 inclusions of fine-grained granitic material, with a semi-schistose 

 structure. These inclusions are of great interest as, when studied, 

 they will probably throw some light on the origin of the rocks 

 which contain them. This slice is cut so as to show a portion of 

 the granite and part of one of these inclusions. On this account 

 the slice may deserve a short detailed description. At a first 

 glance, it will be noticed that there is no hard and fast line 

 separating the inclusions from the normal rock. In fact, the 

 inclusion seems, when examined under the microscope, merely a 

 finer variety of the same rock. The minerals present are identical, 

 their mode of occurrence is the same, with the exception that the 

 quartz is rather poorly represented and hornblende is always 

 absent. However, under crossed nicols, it must be admitted 

 that the inclusions have something more of a clastic appearance 

 than the normal rock. Both orthoclase and a triclinic felspar are 

 present in the inclusions. In the portion of the slide representing 

 the normal granite, a microscopic grain of quartz will be seen, 

 completely surrounded by a fringe of fibrous hornblende. This is 

 in the vicinity of other quartzes and may be taken as typical of 

 the general appearance of the quartz in this granite. No inclu- 

 sions that I ever examined contained quartz at all resembling 

 this occurrence. All the quartzes which I have noticed in the 

 " inclusions " seem surrounded by other minerals, rather than 

 filling up the interspaces between the other constituents as it does 

 in the normal granites. It will be noticed too that under the 

 microscope with crossed nicols, the inclusions show a decided 

 tendency to that structure known as a " mosaic field." The 

 structure of the inclusions is a much nearer approach to a hornfels 



* Observations on the Structure of Quartz-Granites, by Prof. E. Hull, 

 f.r.s.— Geol. Mag., Vol. x., p. 193. 



