W. Maynard Hatchings — Rutile in Fireclays. 305 



MacMahon seems to infer, the trituration of a clay ("without 

 grinding") partly in water, being a gentle operation. But, violent 

 or gentle, I fail to see that it has any bearing on the fact, on which 

 stress is laid, that after separation none of the larger flakes of mica 

 contain any rutile at all ; nor on the conclusion which this fact 

 enables us to draw, in view of what we know of the nature of the 

 materials forming these deposits, that the rutile was not brought into 

 the sediments in the mica, as such. 



As regards the fact that the mica of these "complex flakes" 

 containing rutile is orientated in all directions, I do not look upon 

 it as of much importance one way or other. General MacMahou 

 thinks that if the mica is secondary the " molecules of mica would, 

 at the moment of crystallization, surely have followed the laws of 

 crystallization and have arranged themselves in definite order." 

 This is simply an a. priori supposition as to what ought to take place, 

 and can hardly count as an argument. As a matter of fact, obser- 

 vation of mica which is formed as a secondary product in altering 

 felspar, either in crystals of felspar or in fine felspathic ash-material, 

 seems to show that no such definite order is by any means the rule, 

 but rather in most cases quite the reverse. Such, at least, is my 

 experience with materials of this nature of which I am just now 

 making a special study. 



It is suggested that the micaceous ilmenite may be the source of 

 the rutile. I do not think examination of the materials could lead 

 anybody to this view. I regard this mineral as secondary, and 

 derived indirectly from the same source as the rutile. I do not 

 know that the transparent and translucent micaceous ilmenite as it 

 occurs in these clays, etc., and abundantly in some slates, has ever 

 been regarded as anything but secondary, nor that any original rock 

 has been suggested whence it could be derived clastically. 



Finally, while admitting the full force of some of General 

 MacMahon's criticisms, I venture to think that the subject should 

 be looked at and judged a little more os a ichole, taking in what I 

 might call outside matters as well as details of the laboratory and 

 the microscope. 



Broadly, the matter stands as follows : We have these large 

 and extended deposits of the Coal-measures all apparently similar in 

 nature, derived from similar sources. All the evidence obtainable 

 goes to show that these sources were granites or gneisses. There is 

 not any evidence of any sort to show that any other class of rocks 

 was concerned in supplying the sediment, and I am not aware that 

 any student of them, in the field or in the laboratory, has ever sug- 

 gested another origin for these beds, either wholly or partially. 



A portion of these deposits, the clays, contains these vast numbers 

 of rutile-needles, I suggest that these are of secondary origin, 

 formed in situ, and I think they result from the decomposition of 

 biotite-mica, which can be seen to have formed so lai-ge an item in 

 the original sediment ; because biotite when tested has been found 

 to contain titanic acid, and because it has been observed, under some 

 conditions, to give rise to rutile during its decomposition. 



DECADE III.— VOL. YIII. NO. VII. 20 



