1TETAM0EPHIC ROCKS OF SOUTH DEVOX. 



721 



crystal, which has evidently been broken and suffered some displace- 

 ment of its parts with deposition of calcite along the crack. Similar 

 examples of pressure-effects may be found in various slides. 3tlany 

 of the clear grains in this Bickham specimen, even where not exhi- 

 biting definite cleavage-lines, contain narrow laths of a richly 

 coloured reddish-brown mineral, possibly haematite, which have a 

 uniformity of direction in the grain, as if determined by its cleavage- 

 planes. In another specimen of chlorite-schist, taken from the 

 foundation rocks of the Old Castle near Salcombe, Professor Bonney 

 called my attention to the form and arrangement of the grains in 

 the clear layers. Without magnifying, the folded zigzags of these 

 colourless bands are quite evident across one part of the slide. 

 Under a low power of the microscope their constituent grains show 

 an elongation transverse to the main layer, and with polarizing 

 apparatus an orientation of colours similarly transverse, these cha- 

 racters of form and optical property being therefore due probably to 

 the pressure which bent the layers. 



Certain masses of chlorite-schist occurring in the northern part 

 of the district call perhaps for some special notice. Specimens for 

 the microscope were taken from the points on opposite sides of the 

 main estuary north of Salcombe, which I have called for distinc- 

 tion "Snapes" Point and "Scoble" Point. The usual minerals 

 (chlorite, quartz, epidote) are present, and in the Scoble slide occur 

 some grains of the cleaved mineral and some which seem to be 

 felspar ; we may note examples of simple twinning, and others of 

 multiple twinning after the manner of plagioclase. One very 

 interesting specimen was pointed out to me by Professor Bonney 7 

 where the members of the compound crystal are distorted, waved, 

 and even broken across and displaced — an additional proof of the 

 action of pressure, which had seemed to me marked in this rock even 

 in hand-specimens, and emphasized by the evidence of the microscope- 

 slides. The section of the Scoble rock shows quartz-grains, occurring, 

 for the most part, separated in the chloritic ground-mass, and many 

 of the grains elongated, with their long axes parallel to the lami- 

 nation. In the Snapes specimen knots of quartz appear frequently 

 as if squeezed out into rather long irregular bands, in which the 

 mineral has assumed the ordinary schist or quartzite characters. 

 Some of the separate grains are of very flattened form. In the 

 mass the rock exhibited, throughout, a close compressed look, but 

 was traversed at places by bands of apparently different mineral 

 constitution. The evenness of these layers and the compressed look, 

 taken in connexion with the micro-structure already noted, seem to 

 suggest that the rock had suffered from a pressure somewhat 

 normal to the bands, and that the lamination may have existed in 

 some form in the rock as a previous stratification-foliation. 



2. Micaceo-cliloritic Schists. — An interbanding of some mica- and 

 chlorite-schists in the cliff near Bickham Signal-Station yielded a 

 specimen containing both mica and chlorite, with layers of quartzose 

 and other colourless grains, some cleaved and some exhibiting 

 twinning. Scattered about with epidote are small garnets, abundant 



