Vol. 65.] PETROGRAPHY OP THE NEW RED SANDSTONE. 235 



the cleavage {010}. The long edges are modified by the prisms 

 {110}, and the crystals are terminated by the forms {101} and 

 {001}. The large flat face (010) is normal to the obtuse bisectrix 

 (a), and the axis of elongation (= c) lies in the plane of the optic 

 axes. The pleochroic scheme for these crystals is 

 a — pale straw-yellow ; fc = deep yellow. 

 Angular grains similar to those usually occurring in the Red 

 rocks have been noted by many authors from a variety of sediments, 

 including Cayeux from the Chalk, Rene Breon from the marine and 

 dune-sands of Britanny, Retgers from the dune-sands of Holland, 

 Thiirach from the sands of the kSahara, and Artini 1 from the alluvium 

 of the North Italian rivers. 



Topaz. — Topaz occurs sparingly as angular cleavage-fragments 

 in the Lower Breccias and at some localities in the Pebble-Bed. 

 The flakes are colourless, and give an interference-figure in con- 

 vergent light showing an angle between the optic axes, in air, of 

 about 110°. Usually, they are only thick enough to show the colours 

 of the first order, and are full of gaseous and fluid inclusions. 



Actinolite. — This mineral has been met with as pale-green 

 acicular and fibrous aggregates, usually associated with pink garnet. 

 The pleochroism is distinct, the greater absorption occurring in a 

 plane at right angles to the axis of elongation of the needles. It 

 presents the usual characters of actinolite from metamorphic rocks, 

 and is the only amphibole that is known to occur in the Red rocks 

 of this district. 



III. Physical Characteristics of the Finer Material. 

 The grains forming the matrix of the Lower Breccias are in- 

 variably angular or but slightly rounded, thus presenting features 

 almost identical with those of the larger rock-fragments with which 

 they are associated. In the intercalated beds of sand and sandstone, 

 however, a great difference in the grain is apparent. The particles 

 forming these finer deposits are always well worn, and usually 

 more so than those of the ordinary marine sands or dune-sands of 

 coastal regions. In fact, many samples approximate very closely to 

 the ' millet-seed ' sands of deserts. This feature in connexion with 

 British red sandstones has been pointed out by Phillips, Goodchild, 

 and others. Sands of this type occur at Berry Head, 2 the western 



1 Eiv. di Mill. & Crist, Ital. vol. six (1898) p. 33. Speaking (ibid. p. 41) of 

 the staurolite from the River Adige, he says that it is ' Piuttosto abbondante, 

 quasi sempre in granuli irregolari, a spigoli vivi ; scavse inclusioni, colore 

 vivace, pleocroismo distinto.' 



2 The rock at Berry Head occupies a fissure in the older rocks, and forms a 

 pipe or dyke of fairly compact sandstone. The cementing-material is partly 

 ferruginous and partly siliceous. Similar dykes have been noted in other 

 districts (W. Pengelly, Trans. Devon. Assoc, vol. i, 1864, p. 40 ; also E. B. 

 Tawney, Proc. Bristol Nat. Soc. n. s. vol. i, pt. ii, 1875, p. 162). In my former 

 paper in this Journal I erroneously regarded the Berry Head rock as a 

 possible outlier of Pebble-Bed ; but, as pointed out by Pengelly and impressed 

 upon me by Mr. TJssher, it must belong to an earlier, if not the earliest, period 

 of the New Red Sandstone. 



