166 W. M. Hutchings — Farther Notes on Fireclays, etc. 



orientation. The majority of these complex flakes have all their 

 component flakelets lying flat in one plane ; but some are seen, 

 especially among the coarser material ot F and G, which are more 

 or less globular aggregates, in which the mica lies at all azimuths, 

 those bits seen edgewise depolarizing very brilliantly. 



I may here remark that when the same levigation-process was 

 carried out with a coarser band of the Seaton clay, — the grade of 

 coarseness next following the fine fireclay, — ^just the same results 

 were obtained. A much less relative proportion of the finer material 

 was obtained, of course, but what was got was similarly composed, 

 and the limits of size of the rutiliferous flakes were the same. 



Most patient search was made for flakes which, might allow of 

 tests in convergent polarized light ; but not one could be found of 

 sufficient size which was not complex, and therefore useless for that 

 l^urpose. One or two " figures " which I thought I had obtained, 

 in " sections " of the clays, from rutiliferous flakes, are therefore 

 very doubtful and of no value ; probably due to original muscovite 

 imperceptibly mixed in with the secondary minerals. 



The same difficulty occurs in examining slates. Not in the 

 thinnest parts of the thinnest sections it is possible to make have 

 I ever succeeded in finding a single simple flake of the rutilifei-ous 

 mica. It is all a felted complex of small flakes, exactly similar to 

 the larger of the complex flakes in these clays. 



The study of A, B, C, in conjunction with the coarser grades, 

 leaves no doubt on one's mind that the bulk of the material of the 

 former results from the disintegration of the complex flakes and 

 globular aggregates described; the rutile lies mainly in between 

 the minute component flakelets, and is set free when these are 

 detached, except in relatively few eases of larger single flakelets. 



There will also doubtless be present in the finest slimes more or 

 less of minute flakes of original muscovite, though most of this 

 mineral in this fine state of division has, I think, been absorbed into 

 the new combinations. 



In all the coarser grades there is present a good deal of original 

 clastic muscovite, much more than would be supposed from examin- 

 ation of sections of clay, where much of it is hidden. All this 

 muscovite is perfectly colourless and clear, and free from any trace 

 of rutile. The supposed secondary mica is all very distinctly 

 coloured, mostly yellow, sometimes greenish, and larger flakes are 

 more or less turbid. 



Flakes of altered biotite are also not scarce, now that levigation 

 has set them free. They are relatively large, easily recognized, still 

 considerably active in polarized light and dichroic when seen edge- 

 wise, but flat sections are all quite inactive in convergent light, 

 being all more or less advanced in the process of waste and bleaching, 

 with the same formation of epidote, etc., as described in the coarser 

 material in my former paper. 



No such flakes which can be identified as biotite in any stage of 

 decay contain any rutile whatever. 



There is nothing special to remark about the other minerals in 

 these coarser parts of the levigated clay. Quartz and felspar grains 



