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nicols felsitic matter gives a distinct reaction, the field possessing a peculiar 

 speckled appearance, but the boundaries of the double-refracting particles 

 cannot be recognised. These appearances can be explained, in many cases by 

 the assumption that we are dealing with an aggregate of mineral particles 

 so small as to overlap each other in the thinnest possible sections. It would, 

 however, probably be a mistake to suppose that in every case this felsitic 

 matter is holo-crystalline. If a small quantity of amorphous matter were 

 present it might be impossible to recognise it. All that we can say with 

 certainty at present is that the individual constituents of this perplexing 

 substance are of ultra-microscopic dimensions. 



If the term felsitic be used in a macroscopic sense it will include the 

 groundmass of the micro- granites, granophyres and felsites proper. 



The microlitic, crystallitic and spherulitic textures do not call for any 

 detailed description in this connection. In a true glass the only texture 

 which requires notice is the perlitic. This is due to a number of more or less 



circular or spiral cracks which are produced in consequence of contraction at 

 the time of consolidation. The case figured is that of a pitchstone from 

 Meissen, in which a certain amount of alteration has taken place along the 

 cracks, thus making them more conspicuous than is usually the case. Rocks 

 possessing this texture are often termed perlites ; but, as they possess the 

 other characters of pitchstones and obsidians, and the texture is one which 

 can be produced in other substances, such for instance as Canada balsam, it 

 seems better to adopt the suggestion of Mr. RUTLEY, and use only the 

 adjective perlitic. The rocks in question would then be termed perlitic 

 pitchstones and obsidians. 



In dealing with the textural characteristics of igneous rocks we have not 

 only to take into consideration the mutual relations of the individual 

 constituents, but also their relations to the rock-mass as a whole. In the 

 normal plutonic rocks the texture as a rule is uniform, there are no directions 



