OPPONENTS AND OBJECTIONS. 181 



the walls more broken by cleavage planes than usual. 

 The portion selected shows a part of one of the 

 chambers filled with serpentine, which presents the 

 usual curdled aspect almost impossible to represent 

 in a drawing (s). It is traversed by a branching 

 vein of chrysotile (s r ), which, where cut precisely 

 parallel to its fibres, shows clear fine cross lines, 

 indicating the sides of its constituent prisms, and 

 where the plane of section has passed obliquely to its 

 fibres, has a curiously stippled or frowsy appearance. 

 On either side of the serpentine band is the nummu- 

 line or proper wall, showing under a low power a 

 milky appearance, which, with a higher power, 

 becomes resolved into a tissue of the most beautiful 

 parallel threads, representing the filling of its tubuli. 

 Nothing can be more distinct than the appearances 

 presented by this wall and the chrysotile vein, under 

 every variety of magnifying power and illumination ; 

 and all who have had an opportunity of examining 

 my specimens have expressed astonishment that ap- 

 pearances so dissimilar should have been confounded 

 with each other. On the lower side two indentations 

 are seen in the proper wall (c). These are connected 

 with the openings into small subordinate chamberlets, 

 one of which is in part included in the thickness of 

 the slice. At the upper and lower parts of the figure 

 are seen portions of the intermediate skeleton traversed 

 by canals, which in the lower part are very large, 

 though from the analogy of other specimens it is 

 probable that they have in their interstices minute 



