Dr. C. 0. Trechmann — " Hypersthenife" of Carrock Fell 211 



Mr. J. C. Ward,^ and which is described by him generally as " a 

 coarsely crystalline compound of plagioclase felspar and hypersthene, 

 with scattered grains of titaniferous iron oxide, and more or less 

 quartz," remarking that " the hypersthene may be replaced by a horn- 

 blendic mineral or may occur in conjunction with it." It is a rock 

 of rather coarse grain, consisting macroscopically of dull white 

 crystals of plagioclase felspar with a greenish or bluish-green cast, 

 some parts clear and vitreous with twin striations ; very dark olive- 

 green diallage in irregular grains, occasionally forming crystalloids 

 with definite outline up to one-quarter of an inch in length, and 

 rarely with any distinct metallic lustre on the cleavage faces (Mr. 

 Teall states that the metallic lustre is pronounced in the weathered 

 parts of the rock) ; large black grains and octahedrons of magnetite, 

 perhaps in part ilmenite ; a considerable quantity of white or greyish 

 quartz in large grains ; a soft micaceous decomposition product of 

 paler colour than the diallage ; lastly, a few minute elongated hexa- 

 gonal crystals of a transparent light grass-green and rather soft 

 mineral, which appears to be apatite. 



The felspar is kaolinized on the weathered side of the specimen, 

 leaving the diallage in a soft brownish-green altered condition, 

 apparently serpentinized. 



The microscopical analysis of a section cut from the specimen 

 gave the following result : — 



1. Plagioclase, probably labradorite, in large crystals, which were 

 highly altered to a j^ellowish fine-grained substance, with aggregate 

 polarization, and here and there intersected by fine veins of chlorite 

 or serpentine, leaving clear and perfectly fresh portions made up of 

 broad twin lamellae, crossing one another in two directions. The 

 dark microliths so common in labradorite are wanting. 2. Diallage 

 in irregular patches, finely striated by cleavage fissures and dark 

 interpositions. Faint cleavages in other dii'ections also visible. Some 

 parts, especially near the edges, were without interpositions. No 

 twins. Colour pale brown, no pleochroism, active polarization, like 

 augite. Occasionally a lamellar polarization, probably due to altera- 

 tion. In sections more or less parallel to the klinopinacoid the 

 position in which extinction took place between crossed Nicols gave 

 angles varying between 23^° and 30^° with the vertical axis, i.e. 

 direction of striation, of the crystals. No hornblende in conjunction 

 with diallage. 3. Hornblende (?). A few minute grains were 

 strongly pleochroitic, from bluish-green to yellowish-green, distinct 

 cleavage and a somewhat rough surface. Extinction gave 9° with 

 the direction of vertical axis. This may be hornblende. 4. Ser- 

 pentine. A large portion of the augitic or hornblendic constituents 

 of the rock is more or less completely altered to bright green ser- 

 pentine, slightly pleochroic with aggregate polarization ; a part may 

 be chloritic. 5. A micaceous mineral is repi'esented by a small 

 number of minute irregular grains with wavy black striations. 

 Dichroism distinct, dark bluish-green and yellowish brown. Extin- 



1 Ou the Granitic, Granitoid and Associated Metamorphic Rocks of the Lake- 

 district. Pts. iii. — v. Quart. Joum. Geol. Soc. vol. xxxii. (1876) p. 21. 



