144 J. SLADE ON SECTIONS OF COAL. 



marine glue ; the marine glue used, requires careful selection; that 

 usually sold frequently contains particles of the undissolved 

 materials, which are visible enough under the microscope. 



However, having obtained the right sort, cut thin slices ; lay 

 them upon the glass slip, and melt over a flame; when thoroughly 

 melted, drop the specimen (the polished surface being downwards) 

 into it, and press out the air bubbles When air bubbles appear 

 between the glass and the surface of the coal — which they often do, 

 and sometimes prove very annoying — they must be got rid of ; 

 otherwise it is useless to proceed, for long before the specimen is 

 thin enough to show structure, the coal over the air-bubble comes 

 away, leaving a hole. If they be not present, the preparation may 

 be proceeded with, first reduced on sandstone, and then finished by 

 pumicestone ; and after scraping away the superfluous marine glue, 

 mounting in Canada balsam, and covering in the usual way. 



As the preparing goes on, the specimen will be occasionally 

 viewed under the microscope. The first to appear will be the spore 

 cases, and a careful continuance of the grinding will finally render 

 the spores visible. 



Spores and spore cases are to be found in every successful pre- 

 paration of coal ; but their relative proportions and degree of pre- 

 servation vary considerably ; thus Wigan Cannel almost entirely 

 consists of spores, very few spore cases. Bradford coal, 6pores and 

 spore cases in nearly equal proportions. Silkstone coal, spore cases 

 few, and much compressed spores in abundance. Moira coal, Lei- 

 cestershire, spore cases beautifully preserved, and in some, spores 

 in situ. Dalkeith coal, the same, the spore cases, on the whole, 

 being slightly more compressed. Wallsend, spore cases much com- 

 pressed and altered, and mixed up with a quantity of grit and 

 amorphous bituminous matter. White coal, of Australia, consists 

 almost entirely of spore cases. 



