280 PROF. T. G. BO^NEY AND MISS C. A. EAISIX ON [Mny 1899, 



with the longer axes of the ellipsoids. Some patches occur in the 

 fields east of Padog. West of the road a few small patches, much 

 squeezed, are scattered among the serpentine.^ Then important 

 masses are found immediately north of the track leading to Cerig- 

 moelion. 



II. Seepentine. 



(a) Macroscopic Characters. 



(1) Normal Varieties. 



Hand-specimens of the serpentine generally do not show very 

 marked differences. The rock is of a dark, dull green colour, some- 

 times with a tinge of purple, mottled with a rather bright green 

 translucent substance resembling ' noble serpentine,' which occa- 

 sionally dominates, especially if the specimen shows marked signs 

 of pressure. Sometimes it is compact and rings under the hammer, 

 sometimes it is pitchy in aspect and is rather ' crackled/ possibly 

 indicating the approach to a junction. 



Some small bosses, however, in the fields east of Plas-coch afford 

 a fairly distinct variety. This has a glittering appearance, as if it 

 abounded in minute crystalline flakes or grains with cleavage- 

 surfaces, and the rock feels more gritty than ordinary serpentines 

 (hardness about 3-75 to 4). It resembles an impure variety of a 

 serpentine, but is etched by hydrochloric acid as readily as normal 

 specimens of that rock. More marked varieties are due to the 

 conspicuous occurrence of accessory minerals, of which enstatite 

 and diallage are the commoner. A cleavage-surface of one or the 

 other can often be seen here and there in the serpentine, and where 

 this evidence is wanting, their presence is proved by microscopic 

 examination. These accessory minerals appear to be sporadic in 

 distribution, and not limited to any locality. The most remarkable 

 examples are those in which the included crystals are lustre-mottled, 

 as in a crag south of Cerig-moelion, and in a cliff south of 

 Rhyd-bont (see pp. 279, 285). At the last-named locality the crystals 

 are exceptionally large, sometimes apparently 5 inches long, and the 

 exposed cleavage-surfaces flash brilliantly in sunlight. They are 

 scattered over a roughly vertical cliff-face, which extends for about 

 12 yards along the northern shore of the inlet. 



Iron-oxide occurs, but, as can be seen even in hand-specimens, it 

 is very variable in distribution. Sometimes it is scattered uniformly 

 in small crystalline grains, sometimes it forms nests or clusters 

 closely massed over a few inches.^ We proved some to be magnetite, 

 but some of the grains are apparently a less opaque spinellid; while 

 other grains, which with reflected light are somewhat copper-coloured, 

 are possibly awaruite. 



^ The ' green schists' south of the serpentine form considerable masses, many 

 of which have an aspect resembling that of a gabbro. 

 - As, for example, on one rock near Rhyd-bout. 



