462 SHALE. 



This substance sometimes contains impres- 

 sions of wood and of fishes. It is of such limited 

 occurrence that it might perhaps more properly 

 have been ranked, -like Tripoli and other matters, 

 with the minerals of a mineralogical system. 



SECOND DIVISION. 



Compound. 



A.. Argillo-bituminous. 



a. Slightly impregnated with inflammable 



matter. 



b. Highly impregnated with bitumen so 



as to be combustible : accompanies 

 coal. Black and also brown. The 

 latter is Kimmeridge coal. 



B. Argillo-calcareous containing so much car- 

 bonat of lime as to effervesce with acids. 



Some of the varieties of this, are the marie 

 slates of certain mineralogists. As these sub- 

 stances are not very distinct, they are again intro- 

 duced under the head of marie. 



C. Argillo-micaceous; containing a conspicuous 

 proportion of mica. 



D. Arenaceo-micaceous ; containing a large pro- 

 portion both of sand and mica. With the former, in 

 Sky. 



