NERBUDDA DISTRICT. 



137 



attain a very considerable thickness in the aggregate, and occupy large 

 areas at the surface. 



The boundaries of this sub-division cannot be laid down with preci- 

 sion, any more than those of the calcareous group, into which it merges 

 on the one hand, while on the other it gradually passes into the* arena- 

 ceous schists ; a fact which must of course be borne in mind when the 

 thickness of the beds or the area exposed is spoken of. These argillaceous 

 schists are chiefly micaceous as a whole, the garnetiferous and the 

 andalusite-schists being the most characteristic features of the series. 



In the group which is characterised as arenaceous, and which we 



mean to include all the schists not referable to 

 Arenaceous schists. 



either of the former sections, a somewhat hetero- 

 geneous set of beds are collected together under one head. All are how- 

 ever fairly described as siliceous in contradistinction to the argillace- 

 ous and calcareous sets. We find a very great development of true 

 schistose quartzite, in many parts of the area of the crystalline rocks. 

 This rock is often very massive in spite of its laminated structure, but 

 generally divides into flags more or less regular and is in several places 

 quarried for roofing as well as flooring. The whole set of hornblende 

 schists and rock is also included in this section. Many varieties exist, 

 often characterised by the presence of schorl, and in a few instances by 

 actinolite. Besides these, which are characteristic of beds as such, other 

 minerals, (Tremolite for instance) occur as accidental ingredients 

 throughout whole sections. Besides these, runs of talcose schists and 



of tolerably pure steatite, occur among the impure 

 Steatite. .»','••. 



calcareous portion of the series. 



True slaty cleavage is of rare occurrence and ill developed. 



Much jointing occurs, and has in many cases been observed with 

 care : the number of these observations is however insufficient to warrant 

 any satisfactory conclusions as to the prevalent systems under which 

 the facts might be arranged. Considerable complication exists, the 



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