79 



noticed that the pointed ends of the crystals project away from the 

 sides of the crack or fissure which they Hne. 



(4.) Lastly, Vein Quartz occurs in indefinite lenticular 

 masses and strings among the strata of many geological formations. 

 Thus, occasionally it may be seen to occur between the planes of 

 bedding of stratified rocks, more frequently, however, traversing 

 those planes in an irregular and stringy manner, and sometimes 

 much developed along the cleavage planes, as may be seen in the 

 Skiddaw Slate between the summit of Hindscarth and Scope End. 



Quartz as a Rock-Constituent. 



(a) Of Stratified Rocks. 



(b) Of Unstratified Rocks and Volcanic Rocks. 



(a) Of Stratified Rocks. 



In the Skiddaw Slates there are many parts — especially the 

 lower, seen on Whiteside and Grasmoor — which have been pro- 

 duced by sandy or gritty deposits, and the grains of quartz may 

 frequently be distinguished clearly with the naked eye. Again, in 

 a well marked bed of grit, in the upper part of the Skiddaw Series, 

 to be well studied in Great Cockup, north of Skiddaw; in the 

 sides of the northern breast of Skiddaw ; and notably at Lank Rigg 

 and Latterbarrow, in the south-west of the Lake District, the grains 

 of quartz frequently approach the size of small pebbles. In all 

 these cases the quartz fragments are more or less rounded, showing 

 that they have been rolled in the water, and are formed of white 

 quartz, such as occurs in veins, or such as may be won from the 

 disintegration of granite. Even in the clay-slate proper the 

 microscope reveals the presence of small grains of quartz amongst 

 the aluminous matter. 



In some of the beds of Carboniferous Limestone that wrap 

 round the mountainous tract, quartz occurs both in the form of 

 small pebbles, and of curious amorphous masses very similar to 

 the flint in chalk, but known as chert. In the sandstones inter- 

 stratified with the Limestone, quartz in more or less rounded grains, 

 is the chief constituent In the Penrith Sandstone, of younger age 



