TF". M. Hatchings — Clays, Slates, and Contact-Metamorphism. 37 



old and were made when the determination of alkalies was not so 

 easy and so accurate as it has been since the Lawrence Smith method 

 came into general use. In many analyses, again, alkalies were simply 

 determined "by difference," and the figures are worse than useless. 

 In many other cases potash only is given, and it is not too much to 

 say that many " technical " analyses are not carefully enough made 

 to render them available for scientific purposes. 



It would not serve any useful purpose here to quote a large 

 number of analj^ses of " fireclays," but the following figures may 

 be of interest. They give the average percentages of silica, alumina, 

 and potash in a series of eight analyses made by Mr. E. Eiley on 

 clays from the Dowlais Coal-field. Mr. Riley's name is an assurance 

 of the accuracy of any analyses made by him : — 



Silica. Alumiua. Potash. 



Maximum 67-12 34-76 4-19 



Minimum 44-25 21-18 1-21 



Average 53-39 28-91 2-11 



It may be remarked that Mr. Eiley has not determined soda, 

 though this is present in all fireclays, — according to my own 

 examinations being usually about one-fourth of the amount of potash. 

 Moreover, the average amount of water and organic matter in the 

 above analyses was 11 '63 per cent. The loss by ignition of an 

 average slate is about 3 per cent, only, so that for purposes of 

 comparison the alkali in the above figures would have to be increased 

 about 8 per cent. 



I have made with the greatest care a series of six analyses. For 

 this purpose I used the material in my possession in the form of 

 a number of cores from a bore-hole put down in the Coal-field at 

 Aspatria, near Carlisle. The bore-hole was 800 feet deep, and the 

 specimens represent various beds of sandstone, shale, and clay, with 

 the gradations between them. For microscopic examination I have 

 made sections of this material from eighteen different points. 



The analyses of the sandstones and very quartzy clays and shales 

 would have no special interest. I have selected samples of very 

 fine-grained clay representing beds at various depths from 330 feet 

 to 685 feet, and one bed of more quartzy material. None of these 

 were in contact with Coal. The clays are very compact and hard. 

 Ground with water they are exceedingly plastic. 



No. 1 contains a good deal of quartz, which is seen under the 

 microscope as evenly dispersed grains. Nos. 2-6 are among the 

 finest-grained clays I have seen. The quartz present is so finely 

 divided that it cannot be detected at all among the mica, etc., in 

 slides, and can only be found by levigation. No felspar can be 

 detected at all. They are the most completely micaceous samples in 

 my possession, and it is safe to say that very nearly all this mica is 

 newly formed in situ. 



The analyses were made on samples dried at 220° F. 



Titanic acid has not been determined, and is therefore contained 

 in the silica and the alumina of the analyses. Taking the careful 

 research of Mr. Eiley on the presence of titanic acid in clays as a 



