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SCIENCE-GOSSIP. 



tion, one flake being almost broken in two, the 

 fracture or rupture not having gone quite through. 

 The chief matters of interest in this slide are the 

 inclusions contained in the quartz. These are 

 very numerous, and vary greatly in shape. Long 

 fluid pores are seen, needles of apatite, zircons, 

 gas pores, and fluid pores, with bubbles and 

 cavities of all shapes and sizes. Some cf the 

 crystal-shaped inclusions resemble zircons, but 

 are constricted in a peculiar way in the middle. 

 A little biotite and pyrites are also found in this 

 rock, its brownish colour probably being due to 

 the latter mineral. 



An examination of a thin section of aplite with 

 the schistose structure shows that its laminated 

 character is brought about by the presence of 

 small flakes of biotite, having the usual ragged 

 edges and polarizing in strong reddish-brown and 

 green colours. The rock itself is a similar one to 

 the aplite just described, but the porphyritic 

 crystals do not seem quite so common. Some of 

 the felspar crystals are found twinning on the albite 

 system, and smaller lath-shaped crystals are to be 

 seen in the granular mosaic base of the rock. 

 Reddish - brown and yellow garnets are again 

 present. 



The inclusions in the quartz are very interesting. 

 They comprise zircons (some being fairly large 

 ones), glass inclusions, apatite, pseudomorphs of 

 different kinds, schiller inclusions of iron oxide, 

 glass inclusions devitrified, and one or two larger 

 negative crystals containing bubbles and cubes. 



Another variety of rock, of which I brought a 

 specimen, appears to be dolomite, or a mixture of 

 dolomite and calcite. A fresh fracture shows this 

 to be crystalline of a light yellowish-brown colour, 

 with fine veins and minute specks of pyrites and 

 lead ore. The weathered surface of it is, however, 

 of a deep reddish-brown, somewhat resembling 

 haematite in colour. 



On first examining a thin section under the 

 microscope, I came to the conclusion it was all 

 calcite, and the strong, double refraction, cleavage 

 angle, and general characteristics evidenced such a 

 rock. On making a chemical examination of the 

 hand specimen, however, I found that nitric acid 

 had no effect either on the weathered surface or 

 the fresh fracture. The rock, therefore, could not 

 be composed of calcite, and must be a variety of 

 dolomite. 



On making a more careful examination of the 

 slide, I found many comparatively wide fissures, 

 some filled with ordinary calcite, others with 

 amorphous quartz, some with iron oxide, and 

 others containing minute crystals of dog-tooth 

 spar. The main mineral was a clear one, marked 

 with cleavage lines and, occasionally, with large 

 patches of some variety of iron oxide of a strong 

 orange colour. 



These observations would tend to show the rock 

 to have been originally a limestone which has 

 undergone a metasomatic change, shrinkage having 

 occurred during the process, which is a common 

 result of dolomitization. The cracks had subse- 

 quently been filled with quartz, iron, and secondary 

 calcite of different kinds. 



Making Microscopical Sections. 

 In concluding my remarks on a few of the 

 petrological features of the Isle of Man, I would 

 allude to the rock sections which I have used for 

 the purpose of the examinations referred to in this 

 article. All of these I have myself made by the 

 somewhat slow process of grinding "chips" down 

 with coarse emery on a steel plate. They were 

 then finished off with flour of emery on a sheet of 

 plate glass. Although this process is a somewhat 

 long one, and requires a great deal of patience, yet 

 it has its advantages, enabling one to compare the 

 relative hardness, texture, etc., of the different 

 specimens one may be engaged upon. 



The hardest and densest rock which I have 

 mentioned was the quartzite from Port Soderick ; 

 but at the same time it was the most satisfactory 

 one, since its exceedingly fine texture kept it from 

 breaking when getting very thin. The normal 

 basalts, too, were very hard, and took a long time 

 to make, but the same remark applies to them 

 as the quartzite. They were, generally speaking, 

 so fine of texture as to be capable of being ground 

 very thin, not breaking up either during the 

 process of grinding, or removal from the " rubbing- 

 glass " to the micro-slide. The same may be said, 

 in a modified tone, of the basalts, slightly 

 decomposed ; but the fragmentary rocks were very 

 awkward ones to work. They usually broke up 

 into three or four pieces, when being re-heated and 

 properly mounted, owing to the adhesion between 

 the lapilli and ground base being exceedingly small. 



The ordinary granites from Foxdale were the 

 worst rocks of which I had to make slides. They 

 were exceedingly brittle, breaking up in all 

 directions when getting thin and being ground, 

 others breaking when being mounted. Some of 

 them were completely useless, and the manufacture 

 of these slides was by no means satisfactory, this 

 probably being due to the coarse nature of the 

 specimens. 



The aplite varieties were rather awkward ones 

 to work, but from another cause. During the 

 process of finishing with fine emery, this was apt 

 to "soak" into the section, which then had to be 

 very carefully washed before being mounted. 



The diorite, trap, and pebble sections generally, 

 were good ones to make, being capable of very fine 

 rubbing, and not breaking during fixing. 



The easiest slide made was a section of the clay 

 schist from Langness Point. Owing to its exceed- 



