On the Fissure-InclusioJis. 107 



schist, by the experiments of Pfaff. One of the most careful 

 authorities, Ferdinand Zirkel, states that " there can be no 

 doubt, that, as in the prepared thin sections, so also within 

 mountain-masses, the same movements are going on : any 

 block of granite contains in its quartz-grains millions of fluid- 

 inclusions, and in numbers of these — perhaps during millions 

 of years — the restless bubbles have been vibrating." 



The position and distribution of the liquid-inclusions may 

 vary greatly within each mineral-grain. Occasionally they 

 are found in a crystal in parallel encircling rows, in the 

 planes of crystalline envelopment, e.g. parallel to the prismatic 

 faces of a quartz-crystal. But their ordinary arrangement 

 and number is very irregular. Sometimes they are rare and 

 isolated, so that but one or two may be detected in the same 

 field. More commonly, however, they occur in cloudy masses, 

 or in planes, which appear as rows or narrow bands, either ra- 

 diating from a little central cloud, intersecting, or parallel. 



The views of one of the earliest investigators, H. Vogelsang, 

 may be understood from the following quotations,* in reference 

 mainly to the fluid-inclusions in the quartz of the porphyries: 

 *'The water-pores for the most part are so grouped together 

 that they appear spread out upon plane surfaces; nevertheless, 

 the clefts really connected with them are not always distin- 

 guishable I consider them as cavities which in most cases 



have been not quite filled up with fluid by secondary injection. 

 ....The question presented is this: if a fluid rises up or cir- 

 culates through a capillary cleft by capillary force, and this 

 cleavage-plane at the same time breaks through larger cavi- 

 ties, must these cavities be then completely filled with fluid by 

 capillary force ?. . . . It ought not to be said of this explanation 

 that it answers for all cases; especially is there probably pre- 

 sented in this connection ... .a distinction full of significance 

 between the rocks of the porphyry group and of the granitic 

 forms (pp. 155 — 156). So far as my observations go, the 

 fluid-inclusions lie in great predominance upon cleavage- 

 planes and are always very much smaller than the solid in- 

 closures already considered. On the other hand, in their turn, 

 ....the decidedly solid inclosures occur in quite the same 

 form, distribution, and size as the fluid, and, indeed, there may 

 perhaps be this general distinction, that the minute inclusions 



*Philosophie der Geologic. Bonn, 1867. 



