164 W. M. Hutchings — Further Notes on Fireclays, etc. 



III. — FuETHEE Notes on Fieeolays, etc. 

 By "W. Maynakd Hutchings, Esq. 



THESE notes are in continuation of my former paper " On the 

 Probable Origin of some Slates " (Geological Magazine for 

 June and July, 1890). Since its publication 1 have endeavoured to 

 obtain a little further knowledge of the constitution of the fireclays 

 of the Coal-measures, which I regard as so well calculated to throw 

 light on the origin of many slates, and especially 1 desired to get, if 

 possible, a little more evidence as to the supposed regeneration of 

 mica in them, in connexion vpith the intimately associated question 

 of the rutile-needles. 



With this object 1 have tried to get as good a separation of the 

 components of the clay as the very unfavourable nature Of the 

 material will allow, and this I have done by means of a rather 

 prolonged and tedious course of what may be called "fractional 

 levigation." This may be carried out in various ways, but the 

 method I have found best suited is suspension of thoroughly dis- 

 integrated clay in water in large beakers, and syphoning off the 

 suspended portion after appropriate periods of settlement. 



I'he results of such levigation, though naturally very imperfect, 

 still provide a material for microscopic examination from which 

 some information may be had which could not so well be obtained 

 from " sections " of clay, and which to some extent supplements and 

 confirms what was formerly observed. 



Taking again the fireclays of the Cliffs at Seaton, described in my 

 former paper, about a cubic inch of the finest-grained bed was used. 

 It was air-dried and crushed to powder, but not ground. It was 

 then reduced to fine mud by crushing gently in a mortar with water, 

 and finally left several days in water in a beaker, with, frequent 

 agitation, to insure as complete disintegration as possible. Pre- 

 liminary trials showed that a sufficient degree of classification for 

 my purpose was obtained as follows : — The whole was well stirred 

 up in a beaker (11 inches deep by 6 inches wide) and two-thirds of 

 the contents syphoned off after one and a half hours. This was 

 repeated very many times till practically nothing more was taken 

 over. The united material so obtained was again differentiated by 

 suspension in water and drawing off after half an hour, and this 

 second portion was again treated in a similar manner. Thus, three 

 divisions of the first, finest, part were obtained, A, B, and C. 



The residual original clay was next separated by repeated drawing 

 off after 15 minutes' settling, and the portion drawn off was divided 

 into two by a similar process, giving D and E. 



The next stage was to draw off after two minutes' settling, and 

 again divide the resultant part into two, giving E and G, leaving a 

 final coarsest residue of the original clay, H. 



Nothing is obtained from these fireclays at all approaching in 

 fineness what is observed when fresh deposits, and some recent 

 clays, are suspended in water ; material which remains many days 

 in suspension. Everything settles in a few hours, and such original 

 fine slime is long since consolidated and altered into denser matter. 



