TRANSACTIONS OF SECTION C. 573 



The interstitial matter contains extremely minute microlites and skeleton 

 crj-stals of felspar, griiins and skeletons of ina<rnetite, and an indistinct brownish 

 granular substance. It is not possible to recognise, even with the highest powers, 

 any true glass. This interstitial matter occurs in more or less angular patches 

 wedged in between the otlier constituents, and gives to the rock the structure for 

 which Professor Rosenbusch has proposed the term intersertal. The rock itself 

 would be termed by this author a tholeite. 



Now, the peculiar feature to which 1 wish to call special attention is the occa- 

 sional occurrence of spherical patches of interstitial matter. These appear in the 

 thin sections — and they have only been recognised in the sections — as circles. How 

 are these spherical patches to be accounted for ^ An answer to this question is 

 found by studying the ainygdaloids, which have been already referred to as occur- 

 ring in certain portions of the dyke. Microscopic e.\auiination enables us to 

 determine the precise stage in the history of consolidation at which the vesicular 

 cavities, now for the most part tilled with carbonates with or without a narrow 

 border of chalcedony, were formed. Their development evidently displaced the 

 lath-shaped felspars, for these are often arranged tangent ially with reference to the 

 bubbles ; but it produced no etlect on the disposition of the constituents of the in- 

 terstitial matter. It appears, then, that the gas bubbles were produced after the 

 formation of the porphyritic constituents, the augite and the lath-shaped felspars, 

 but before the consolidation of the interstitial matter. It is possible that their 

 development was due to the relief of pressure consequent on the rise of the semi- 

 liquid mass in the crack. If so, then they are analogous, so far as their mode of 

 formation is concerned, to the bubbles which arise in the contents of a soda-water 

 bottle as the cork is partially removed. 



Now, the spherical patches of interstitial matter agree in form and size with 

 the amygdaloids, and to account for them we have only to suppose that the portion 

 of the mass which was liquid at the time of their formation, oozed into some of the 

 vesicles owing to the absorption, escape, or condensation of the gas. That this is 

 the true explanation is proved by the occurrence of cavities which have been only 

 partially filled up. 



The last act to which we have to call attention was the filling up of the cavities 

 remaining empty after final consolidation with chalcedonv' and carbonates. 



We may summarise the history of the rock so far as it is recorded in micro- 

 scopic structure as follows : — 



1. Development of granular aggregates of a felspar allied to anorthite under 



plutonic conditions. 



2. Addition of felspar substance to the external portions of the granular 



aggregates, and the consequent production of crystalline form. 



3. Development of lath-shaped felspars. 



4. Separation of augite. 



5. Formation of vesicles owing to the separation of gas from the magma. 



6. Partial or complete filling up of some of these vesicles with interstitial 



matter. 



7. Consolidation of the interstitial matter. 



8. Filling up of the vesicles remaining empty after final consolidation with 



carbonates. 



10. Observations on the Greenland Ice-sheet. By Dr. Fridtjof Nansen. 



The scientific results of the expedition cannot at present be stated, many 

 observations not having been worked out by the special savanfn to whom they have 

 been submitted. There are, however, some geological points which even at present 

 are prominent, and though I am no geologist, I shall mention some of those 

 which, according to my view, are of interest. 



The shape of the inland ice is of importance. Many geologists have suggested 

 that the interior of Greenland is ice- and snow-clad, but there have been others 

 who were of the opinion that it was not snow-clad ; amongst the latter the famous 

 Nordenskiold. This prominent explorer of Arctic regions did not believe that the 



