96 Q.UARTZ ROCK. JASPER. 



The upper transition or mountain limestone in England is particu- 

 larly metalliferous ; the principal ores are those of lead and zinc ; 

 they occur commonly in veins. Nearly all the lead obtained from 

 the English mines is found in the mountain limestone. Ores of cop- 

 per sometimes occur in this limestone. 



Many of the fossil organic remains, both in the upper and lower 

 transition rocks, are of genera that are not found in the secondary lime- 

 stones. Some of the upper beds seem almost entirely composed of 

 encrinites : madrepores and corallites occur abundantly in the middle 

 part of this formation. 



(Quartz Rock — Rocks composed entirely of crystalline grains of 

 quartz, sometimes occur among primary and transition mountains. 

 Certain causes appear to have operated locally, and separated the 

 quartz and felspar of granite into masses of considerable size. The 

 quartz rock in the county of Wicklovv I observed to be formed of 

 what is called greasy quartz, similar to that in numerous veins in the 

 mica slate, near its junction with granite in the adjacent mountains, 

 and is probably cotemporaneous with the veins. According to Dr. 

 Mac Culloch, the quartz rock in many parts of the Highlands, pre- 

 sents evident indications of being composed of fragments and round- 

 ed pieces again united, and is in fact a quartzose greywacke or grit. 

 Part of the Lickey Hill, near Bromsgrove, is composed of granular 

 quartz ; and similar beds occur near the village of Hartshill, in War- 

 wickshire, between Atherstone and Nuneaton. Quartz rock, as dis- 

 tinguished from quartzose gritstone, is an inconsiderable formation, 

 and may with more propriety be referred to the Transition, than to 

 the Primary Class. 



Jasper. — This mineral is of rare occurrence as a constituent part 

 of beds, or of mountain masses; it differs little from a siliceous flinty 

 slate, but is generally coloured red, brown, or yellow, and is opaque. 

 It contains a large portion of the oxide of iron in its composition. 

 The beds of shale in coal mines that have taken fire, are sometimes 

 converted into a substance in every respect resembling jasper. There 

 are beds of jasper of considerable magnitude in some parts of the 

 Appennines, covered by rocks of serpentine. In some situations, beds 

 of slaty jasper alternate with slate, to which rock they appear to 

 bear the same relation as flinty slate. Lydian stone, which is a black 

 siliceous flint slate, is by some geologists called black Jasper. The 

 only bed of Jasper that I have seen among the English rocks, occurs 

 associated with beds of manganese ore, at Dodscombleigh in Devon- 

 shire. Jasper sometimes occurs in veins, and forms nodules in basal- 

 tic rocks. There can be little doubt that jasper has been, in many 

 instances, formed by subterranean heat, acting with great intensity on 

 beds of argillaceous shale containing iron. 



Hornblende Rock and Greenstone. — -Hornblende rock has been 

 described as associated with primary rocks, it also occurs in the low- 

 er transition rocks. Transition hornblende presents no variety of 



