Vol. 65.] PETEOGEAPHZ OF THE NEW BED SANDSTONE. 233 



Quartz. — Quartz, which generally forms more than 50 per cent, 

 of the New Reel sands, may, for purposes of description, be divided 

 into primary and secondary. 



The detrital or primary quartz may be further divided, according 

 to whether it gives a uniform or an undulose extinction ; and, 

 following Dr. W. Mackie, 1 may be subdivided according to the 

 nature of its inclusions, the inclusions being the best guide to the 

 character of the rock from which the quartz was derived. 



The subdivisions of the detrital quartz are as follows : — 



(a) Quartz with included minerals presenting a regular outline, such as 



apatite, stumpy crystals of tourmaline, etc. 



(b) With acicular inclusions, such as hair-like rutile, fibrous sillimanite, 



and needles of blue tourmaline. 



(c) With irregular inclusions, such as patches of brown glass, small masses 



of felsitic matter, fluid, and gas. 



Secondary quartz is not of common occurrence in the New Red 

 sands of the West of England. It was stated by the Rev. A. Irving 2 

 that the angularity of the grains forming the sands and sandstones 

 of the great Pebble-Bed seemed to be largely due to the deposition 

 of secondary quartz ; but, although a thin coating of this material 

 is occasionally met with, it cannot in any sense be regarded as a 

 general feature. It rarely acts as a cement, but tends to produce 

 doubly terminated pyramidal crystals with a quartz-grain as a nucleus. 



Tourmaline. — This mineral is present in the heavy residues 

 from sedimentary rocks of all ages, but in the New Red rocks it 

 occurs in three distinct varieties. The most common variety is, 

 generally speaking, of a deep-brown colour, and exists either as 

 short stumpy prisms terminated by 'the simple rhombohedron, or 

 as rounded to spherical grains. 



A light-blue variety occurs plentifully in some of these rocks, 

 occasionally in greater abundance than the deeper coloured type 

 mentioned above. It is nearly always acicular, and slender crystals 

 are often grouped together in roughly radiating bundles. The 

 needles show little or no sign of terminal planes, and the groups 

 occur either free, or embedded in quartz after the manner of 

 luxullianite. The point to which the individual rays of a group 

 converge, is often of a brown colour. 



The third variety is evidently connected chemically with the 

 above-mentioned blue acicular crystals, but differs in its habit. It 

 occurs as pale to deep blue, thin hexagonal plates (PI. XII, fig. 6) 

 flattened parallel to the base {HI}. The rhombohedra are repre- 

 sented by narrow planes truncating the horizontal edges. The 

 crystals occasionally show a zonal structure in various shades of 

 blue, and always the emergence of an optic axis. 



The basal plane {111} is one not usually met with on tourmaline- 

 crystals, and it seems unlikely that it would be so largely developed 



1 ' Sands & Sandstones of Eastern Moray ' Trans. Geol. Soc. Edin. vol. vii 

 (1893-99) pp. 148-72 ; see also H. C. Sorby, Quart. Journ. Geol. Soc. vol. xxxvi 

 (1880) Proc. p. 46, and Monthly Microscop. Journ. vol. xviii (1877) p. 209; 

 also J. A. Phillips, Quart. Journ. Geol. Soc. vol. xxxvii (1881) p. 6. 



2 Quart. Journ. Geol. Soc. vol. x'-iii (1892) p. 71. 



