ISO 



a striation parallel to the basal plane. It is interesting to note in one and the 

 same rock the normal diallagic striation and also the similar striation parallel 

 to the basal plane. The replacement of diallage by hornblende has been 

 already referred to. 



The rhombic pyroxene is now principally represented by a green fibrous 

 dichroic mineral, giving straight extinction (bastite). In this alteration 

 product we occasionally find portions of the unaltered enstatite, giving 

 straight extinction, and exhibiting the characteristic pleochroism : pale green 

 for rays vibrating parallel with the vertical axis, and pale brown for rays 

 vibrating transversely. The intensity of the pleochroism is not great. In 

 composition the mineral probably resembles bronzite. 



The felspar varies in its state of preservation in different specimens. In 

 some it is remarkably fresh. In these cases it exhibits fine striation, due to 

 twinning on the albite plan. Two cases of symmetrical extinction on opposite 

 sides of the trace of the face of composition were observed, in which each 

 angle was as nearly as possible 26, making for the double angle 52. These 

 observations confirm Dr. TRECHMANN'S suggestion that the felspar is 

 labradorite. The existence of other felspars is of course not impossible. In. 

 addition to twinning on the albite type we may observe also twinning on the 

 Carlsbad and pericline types. All these types may co-exist in the same 

 individual. 



What is very remarkable in this rock is the occurrence of co/oiirfcss well 

 striated cryxtak of playioclaw in a matrix of elear crystalline quartz. The 

 freshness of the rock in which this occurs precludes the possibility of the 

 quartz being a secondary product. In this respect the Carrock Fell gabbro is 

 entirely different from any of the gabbros previously described. Another 

 feature of great interest is the frequency with which the quartz and the 

 felspar tend to form micro-pegmatitic aggregates. This is best seen in the 

 rocks which form the connecting link between the gabbros and the 

 granophyres. Here we find exquisite examples of the micro-pcgmatitic 

 structure. The section of a twinned crystal of felspar, showing externally an 

 approach to crystalline form, may be seen to be surrounded with micro- 

 pegmatite the felspathic portions of which are twinned in accordance with 

 the central crystal. Here we have a relation similar to that so frequently 

 occurring in the quartz-felsites, where a kernel of quartz is seen to be 

 surrounded by a zone containing quartz which extinguishes simultaneously 

 with the kernel. In. the Carrock rock, however, it is the felspar which forms 

 the kernel. 



The biotite occurs irregularly in the rock. It is characterised by intense 

 pleochroism. Sections at right angles to the vertical axis appear almost 

 opaque when viewed with rays vibrating parallel to the cleavage cracks. 

 This mineral passes into chlorite by alteration. 



The quartz has been already referred to. It plays the role of matrix, 

 and occurs as crystalline grains and also intergrown with the felspar as 

 micro -pegmatite. 



Magnetite or ilmenite is always present and sometimes very abundant. 

 It occurs in crystals, and more frequently in large irregular grains with 



