HARD WICKE'S S CIENCE - G O SSI P. 



217 



QUARTZ^ AS IT OCCURS IN THE LAKE DISTRICT; 

 ITS STRUCTURE AND ITS HISTORY, 



By J. CLIFTON WARD, F.G.S., F.R.M.S., &c. 



{Read at the Annual Meeting of the Cumberland Association for the Advancement 0/ Literature and Science.) 



INTRODUCTION. 



HERE are few minerals 

 more widely spread than 

 Quartz, a chemical com- 

 pound of the two ele- 

 ments, Silicon and Oxy- 

 gen. Common though 

 this mineral is, however, 

 its study opens out 

 questions of deep inte- 

 rest, and may lead us 

 from the contemplation 

 of a pretty piece of rock-crystal to the consideration 

 of subtle and hidden processes in the formation of the 

 crust of our globe. 



1. Geological Distribution. — Quartz occurs among 

 cur lake-country mountains in several forms, but 

 never as a rock by itself, in thick-bedded masses, as is 

 occasionally the case in other mountain tracts. 

 Vein Quartz exists under four conditions. 

 (1.) Constituting the whole thickness of a lode or 

 vein, in which case the latter may be said to be a 

 quartz vein, unless the quartz contains much valu- 

 able ore, such as lead or copper, for then it will 

 more frequently be called a lead or copper vein 

 with a quartz veinstone. Some of these quartz 

 veins are of considerable width — many yards, — and 

 run in straight lines, sometimes for several miles, 

 though often broken by faults. That they contain 

 gold in small quantities is certain, and I have in my 

 possession some small grains of this precious metal 

 extracted from a vein of quartz in Borrowdale. It is 

 well known that gold has been mined in Wales for a 

 great many centuries, but it seems not to exist in any 

 of our Cumberland quartz veins in workable quanti- 

 ties, so far as I have been able to judge. 



(2. ) Instead of being itself a lode or vein, quartz 

 frequently forms strings or courses running in or 

 through a lode formed of various mineral substances . 

 No. 166. 



Supposing the lode to be lead-bearing, it often be- 

 comes an important question how much of the vein- 

 stone may be quartz, and how much calc-spar, barytes, 

 or other minerals ; for the quartz is very much harder 

 than most other constituents of veins, and if the ore 

 has to be extracted entirely from such a matrix, the 

 labour is much increased. Nevertheless, sometime 1 -, 

 even quartzose vein-stuff is quite crumbling, and, 

 when so, the working is comparatively easy. This 

 is the case with several lead-veins occurring in the 

 Vale of Newlands. 



(3.) Quartz, when occurring either as a massive 

 lode or a slender string, is opaque, and generally of a 

 pure white colour ; but it occurs, thirdly, in the form 

 of clear transparent crystals, lining the sides of cracks 

 and fissures either in massive quartz or in some other 

 mineral substance. These crystals have the general 

 form of a six-sided prism, terminated by a six-sided 

 pyramid, but owing to variations in the relative size 

 of the several faces, the appearance of the crystals 

 may vary. Sometimes also they are coloured in 

 various tints, clue to oxides of iron, manganese, &c, 

 mingled with the oxide of silicon, or silica, as it is 

 more usually called. It will be noticed that the 

 pointed ends of the crystals project away from the 

 sides of the crack or fissure which they line. 



(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 strati- 

 fied rocks, more frequently, however, traversing those 

 planes in an irregular and stringy manner, and some- 

 times much developed along the cleavage planes, as 

 may be seen in the Skiddaw Slate between the sum- 

 mit 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, 



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