266 >S^. Ilelmore — MetaTnorphisvi at Carrock Fell. 



At best, then, mountain genesis appears to be merely a feeble 

 expression of the larger telluric properties of om- globe. As such 

 it is fit subject for most rigid analysis. 



The Metamorphlsm of the Carrock Fell Gabbro ? with 

 a Note on the Origin of the Sulphide Veins of the 

 Caldbeck Fells. 



By Sidney Melmore, B.Sc, F.G.S. 



TTTlTHIN the last two years a cutting has been made at the south- 

 ' ' east corner of Carrock Fell, a few yards north of the village 

 of Mosedale, for the purpose of obtaining road-metal. This has 

 opened an interesting section near the margin of the intrusion. 

 The rocks exposed comj)rise two varieties of gabbro and enclosed 

 Eycott lava. Of the two types of gabbro, that next the lava is of the 

 quartz-bearing variety, exhibiting the prevailing dark-green tint 

 in the hand siDccimen, and carries large flakes of biotite. This is 

 succeeded by the same type of gabbro, but in a highly meta- 

 morphosed condition, at once evident in the hand specimen, which is 

 lighter in colour, primarily owing to the decomposition of the felspars. 

 Examination of the first gabbro in thin sections under the 

 microscope shows that it also has been metamorphosed, though 

 in a lesser degree than the lighter-coloured variety. The felspars 

 are of the oligoclase-andesine type ; the central parts of the crystals 

 are in a saussuritic condition, while the ends are free from decom- 

 position. This condition is particularly noticeable in the larger 

 crystals, and suggests secondary deposition of material differing 

 slightly in chemical composition from the original matter, since the 

 crystals show zonary extinction, and the twin-lamellae seem to 

 broaden out somewhat at the ends. The extinction angle is greater 

 for the inner than for the outer zones. The crystals themselves are 

 surrounded and cut up by irregular strings of chlorite. Some of the 

 felsjDars occasionally contain a few minute irregularly shaped 

 colourless plates, depolarizing in colours of a high order, and are 

 doubtless sericite, though they are too small for identification. 

 , The original pyroxene has been converted into pale -green 

 serpentine, which occurs in areas with a more or less sharply defined 

 outline, and having a platy structure. The central parts of these 

 areas are in some cases occupied by small grains of magnetite in 

 a fine-grained mosaic of strongly depolarizing material, and in 

 others by chlorite. Separate fragments of chlorite also occur 

 exhibiting a fibrous structure. Biotite is largely altered to magnetite. 

 This change seems to have progressed from one side of the mica- 

 flake to the other, and can be found in all stages of development. 



A specimen picked out of the heap of material already quarried 

 contained a layer of pectolite, about 3"5 cm. in thickness, surrounded 

 by rock identical in every respect to that already described, except 



