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APPENDIX. 



Mode of Occurrence of the Fossils. — Both the plants and the mol- 

 lusca occur in the grey shales (blue binds) and in the associated nodules 

 of ironstone. In such deposits the mollusca are preserved as internal 

 casts in ironstone, but in the black carbonaceous shales (black bat or 

 bass) the shell itself is frequently present. 



The fish are found as odd, scattered fragments in almost all the 

 shales throughout the sequence; sometimes the remains become so 

 numerous as to form thin ' bone beds ' composed of comminuted 

 bones, teeth, scales, and spines, with, on rare occasions, a more or less 

 complete fish. These bone beds are most common in the black, fissile, 

 carbonaceous shales which so frequently overlie, and pass laterally into, 

 seams of coal, particularly cannel coal. It is from such bone beds that 

 the fish about to be considered have been collected. 



General Section of the Derbyshire and Nottinghamshire Coalfield 

 showing the chief Fossil Horizons. 

 The distribution of the chief fossil horizons in relation to the impor- 

 tant seams of coal, is given in the following general section (in descend- 

 ing order) of the coal-measure sequence : — 



