242 



As I have before mentioned, the specimen has somewhat the ap- 

 pearance of the familiar cone-in-cone structure (see figures, two- 

 thirds of natural size — No. I shows the weathered surface, and No. 

 II a smooth and imperfectly polished one). The surface, which has 

 been carefully rubbed down and smoothed, presents a series of 

 alternating light and dark bands, similar to the banded or rib- 

 boned appearance exhibited by a well-kept English lawn cut by 

 a mowing machine which has been worked in lines alternately 

 up and down the length of the lawn. 



This banded effect is due to the manner in which the light is 

 reflected from the cut edge of the cleavage planes. When held 

 in one position the smooth surface presents a fairly uniform 

 grey tint, but at a certain angle to the light it appears to be 

 made up of alternate light and dark bands, and when reversed 

 in position the light bands become the dark ones and vice versa. 



Thus, in one position the bands a, h, c, d, e, f, q, h, i, j, appear 

 light grey, but when the specimen is turned upside down they 

 exhibit a dark grey shade. 



Even if subsequent examination made on the spot should prove 

 this to be a case of cone-in-cone structure, the specimen will 

 still, I think, be of equal value and interest. 



The chemical composition of the slate is as follows : — 



Hygroscopic moisture . . 

 Combined water (by dif 



f erence) 

 Silica 



Aluminp, ... 

 Ferric oxide 

 Lime 



Magnesia ' 

 Soda 



Potash ... 

 Silica 



Alumina ... 

 Ferric oxide 



Analysis. 

 ...00-48 -^ 



3 37 ) 



385 



10-51 



-22^ 

 3-63 

 4-47 

 •19 j- Soluble in acid 

 traces 

 116 

 •84,, 

 67-64) 



16-77 >• Insoluble in acid... 85-64 

 1-23) 



10000 



Sp. gr. z= 2*75, given by small fragments which had been 

 immersed in water for some time, at 75° F. 



[Two platee.J 



