254 1)K. A. OILLIOAN ON THE PETKOGKRAPHY OF [vol. lxXV, 



several cases has been of such an intense character as to produce a 

 beautiful mylonized structure. Undulose extinction is a striking 

 feature, both of the large and of the small quartz-grains. While 

 examining the Kinderscout Grit (this name is merely used as a 

 convenient term for the lower beds) of Burnsall Fell near Bolton 

 Abbey, I found that much of the quartz of the medium-sized 

 pebbles, and most of the quartz of the finer-grained portions, was 

 either blue or opalescent in tint, and this was best seen where the 

 surface had been bleached by a covering of peaty turf, or where 

 the quartz was surrounded by kaolin. 



A close examination of the other beds of the series, especially 

 the Rough Rock, show that this blue or opalescent quartz is a 

 common constituent. When examined in thin sections under the 

 microscope, the colour is seen to be due^ in some cases to streams 

 of minute rounded or irregular particles which are indeterminable ; 

 while in other cases, needles of rutile (?) occur in vast numbers, the 

 streams crossing at angles of 60° (see PI. XV, fig. 2). Liquid 

 inclusions with movable bubbles are common, both in the quartz- 

 pebbles and in the small grains of quartz. The outline is fre- 

 quently hexagonal or coffin-shaped, and the liquid is usually brown 

 or amber in colour. The types of inclusions will be more fully 

 discussed when dealing with the quartz of the finer material. 



(c) Pebbles of Felspar. 



These pebbles are exceedingly interesting : they usually, when 

 found in the coarser beds, retain a freshness which is remarkable, 

 the lustre of the cleavage-surfaces being such as might be seen on 

 the freshly-cleaved felspars of an un weathered granite. They vary 

 in colour, but the majority are pink or flesh-coloured. The largest 

 individual pebbles obtained by me have measured about 1 x f X | 

 inch, and, curiously, they were embedded in what would be described 

 as fine o-rit, being quite isolated from other pebbles and perfectly 

 fresh quite to the outside. A considerable number of these have 

 been sliced, and have proved to be invariably microcline or 

 microcline-microperthite. Oligoclase is not at all uncommon in 

 the finer material, while orthoclase is but sparsely distributed, and 

 neither of these has been found as pebbles in any of the beds. 



Mr. G-. F. Pickering (of Horsforth), whom I have interested 

 in this question, has kindly allowed me to examine a number of 

 sections which he has made of these felspars, and, in all cases, I 

 have found them to be microcline or microcline-microperthite. 

 Another peculiarity of the felspar is the frequent occurrence in it 

 of blebs of quartz (see PI. XV, fig. 4). 



(d) Pebbles of Pegmatite. 



Almost as common as the felspars are pebbles of pegmatite, 

 some of these measuring ^ inch cube in the coarser beds. This 

 type was apparently found and described by Sorby, but he gives 

 no account of a microscopical examination of any of the pebbles 



