260 Major- General MacMahon — Rutile in Fireclays. 



different optical orientation." If, as I understand, the orientation 

 is promiscuous, this fact seems to point to the deposition of the flakes 

 one above the other by water — ordinary sedimentation — rather than 

 to crystallization in sitA As the molecules of crystals possess 

 strong polarity, the molecules of mica would, at the moment of 

 crystallization, surely have followed the laws of crystallization and 

 have arranged themselves in definite order either as simple or as 

 twinned crystals. If, on the other hand, these " complex flakes " 

 are the mere promiscuous agglomerations of numerous separate 

 individuals, and not single crystals, I fail to see how the fact of 

 this agglomeration supports the contention that the "rntiliferous 

 mica" is a secondary mineral formed after the deposit of the clay. 

 Finely divided fragments of mica suspended in water would be very 

 likely to come together as mechanically mixed agglomerates even 

 before they sank to the bottom. This process, I suspect, is probably 

 responsible for Mr. Hutchings' "globular aggregates in which the 

 mica lies in all azimuths." The attraction which minute particles 

 suspended in water exercise on each other may be observed in a 

 chemist's test-tube every day. 



The author in his examination of the mud prepared in the Labor- 

 atory from the fireclay observed an upward and a downward limit 

 in the size of the flakes of rutiliferous mica, and he attaches con- 

 siderable importance to the fact. " Looking at the facts stated," 

 he writes at p. 167, "the one that appears to have most bearing 

 on the main point concerned is the pretty strict upward limit of 

 size of the rutiliferous flakes." Mr. Hutchings' contention is that 

 the genesis of the rutiliferous mica, and the rutile contained in it, 

 is due to dynamo-metamorphism " posterior to sedimentation " 

 (p. 168), and as the fact stated above seems to be "the main point 

 concerned," it is worth while to consider it in some detail. 



In the first place I would ask whether we can be quite sure that 

 the fact relied on is not in some way due to the process of 

 " fractional levigation " employed. Mr. Hutchings' process involved 

 the crushing of dried clay to powder and subsequent crushing in a 

 mortar with water, followed by repeated washings. After such 

 dynamic treatment, I doubt the value of any theory, as to the origin 

 of the rutile, based on the size of the mica flakes that were finally 

 found to contain rutile compared with the size of the flakes in which 

 this mineral was absent. Free rutile flakes appear to be more 

 abundant (p. 165, para. 2) than those included in mica ; and the 

 author tells us, at p. 166, that "the rutile lies mainly in between 

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

 detached." And as Mr. Hutchings' contention is that the rutili- 

 ferous mica is a secondary product formed subsequent to the 

 deposition of the clay, it follows logically that the free rutile-needles 

 were detached from the mica in Mr. Hutchings' laboratory under 

 the gentle persuasion of his pestle and mortar. 



Considering the rough treatment the mica received in the 

 laboratory or during its previous transport by river, and considering 

 the fact that the bulk of the rutile-needles (p. 165) were free and 



