Maj or- General MacMaJion — Riifile in Fireclays. 261 



detached from mica flakes, it does not seem remarkable to me that 

 the larger flakes shoukl have been landed on the stage of the 

 authoi''s microscope minus their rutile - needles. The flakes of 

 rutiliferous mica appear to have been below xoVoth of an inch 

 in diameter, and owing to their extreme microscopic size may have 

 been protected from abrasion by their superior powers of flotation. 



If mica, as Mr. Hutchings seems to think, was the mother of 

 the rutile, we can hardly suppose that all the mica transported to 

 the Seaton beds was sufficiently rich in titanic acid to furnish the 

 titanium dioxide for the rutile. The titaniferous mica was probably 

 only one of several species of mica transported to Seaton ; and if so, 

 each species may have been characterized by a size of flake peculiar 

 to itself But apart from the question of habit, differences in the 

 size of the flakes may have resulted from another cause. Mr. 

 Hutchings found three species in his fireclay ; muscovite, biotite, 

 and a yellow to green species containing rutile-needles. No evidence 

 has been adduced to show that all three species came from the same 

 parent rock. They may, therefore, have come from different areas, 

 and the differences observed in the size of the flakes may be the 

 measure of the distances travelled by the different species. 



The circumstance that rutile-needles were not found in the 

 muscovite or in the biotite may be owing to the fact that these 

 micas do not contain sufficient titanium dioxide ; and I fail to see 

 what bearing the absence of rutile from the muscovite and biotite 

 has on the points at issue, viz. whether the rutile and the yellow 

 mica are of clastic or secondary origin, and if secondary, whether 

 their genesis is due to ordinary aqueous or to dynamic agencies. 



If, for sake of argument, we admit that the rutile is of secondary 

 origin, can we be sure that any of the species of mica found in the 

 fireclay was the mother of the rutile ? Without disputing Eoth's 

 conclusion that the " separation of the titanic acid of weathered 

 micas as rutile is often enough observed," it seems desirable to call 

 attention to the fact stated by Mr. Hutchings that " micaceous 

 ilmenite " is " rather abundant " in his fireclay. May not this 

 mineral have supplied the titanic acid for the rutile? The fact that 

 some of the needles of rutile are found between the mica "flakelets" 

 does not negative this suggestion, because capillary action is a potent 

 factor in such cases. There is no evidence in Mr. Hutchings' paper 

 to show that any of the mica of the fireclay contains titanic acid, 

 whereas we know that ilmenite contains a large amount — sometimes 

 as much as 59 per cent. — of titanium dioxide. 



Lastly, I would suggest that if the yellow species of mica and the 

 rutile are really secondary minerals, they are products of ordinary 

 aqueous action. I think it will probably be admitted that the fire- 

 clay of the Coal-measures was laid down in water. If so, the soft 

 mud of which it was originally composed must have contained much 

 interstitial water. What has become of this water ? May we not 

 assume that much of it was used up in chemical action on the finely 

 triturated minerals of which the solid portion of the mud was 

 composed ? The water, unless it differed from all other river and 



