STRATIGRAPHICAL ELEMENTS: CRYSTALLINES, ETC. ^^ 



plates or aggregates of triangular sections, and is generally surround- 

 ed by a margin of the greenish decomposition product. A section of 

 this rock as seen in natural light is given in PI. I, fig. 3. 



This rock, together with the next three transitional varieties 

 which will be described, appear to be identical in their mineral 

 composition and structure with those described by Teall (British 

 Petrography, pp. 154, 197, Plates XIX — XXI) from the Scourie 

 dyke, Sutherland. They also shew a perfectly graduated series 

 from a rock of the type just described to a normal, fine-grained 

 hornblende-schist. The plates which I have given are photographic 

 reproductions from drawings made with the aid of the camera lucida. 

 Each represents, therefore, as faithfully as I could do it, an actual 

 portion of the slide as seen through the microscope. 



Nos - iTr§> 3TO EfT> a11 from near Mansehruh. They shew modi- 

 fications of the previous example. They are generally somewhat 

 finer in grain, and exhibit various stages in the change of the augite 

 into amorphous green matter. In the second of the drawings given, 

 shewing these metamorphic changes (PI. I, fig. 4), rock No. -^f r , about 

 half the augite has been so converted, whilst in -^ there is hardly 

 any trace of augite left in the slice. The plagioclase also in the last 

 has become coloured a pale bnff colour, and in addition shews a few 

 traces of crushing. 



The next examples to be described are from another locality, but 

 from a dyke of the same kind. They are selected as being very good 

 examples of the final stage of conversion of the plagioclase-augite 

 rock into a hornblende-schist. 



No. g| r , right bank of Indus river opposite Ghazikot, Black 

 Mountain, can scarcely be distinguished under the microscope from 

 ^f q. In the field it penetrates the gneissose-granite, cutting diagonally 

 across its edges. At its sides it passes into a fissile foliated variety 

 described next. 



No gf^, side of dyke from above locality. It is a foliated variety 

 of the last. The foliation is very noticeable under the microscope, 

 and is of excatly the same character as that of the gneissose-granite, 



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