362 Mr. George Tate on the Cheviots. 



3. Pitchstone porphyry occurs near to Cherry trees, in Rox- 

 burghshire, and in a great cliif near to Yetholm, where it is 

 veined with quartz, coloured with oxide of iron. It is used as a 

 building stone, and the church of Yetholm has been built of 

 it. Essentially the same in composition as felsite, it has a 

 different mineral aspect; it is of a dark grey colour, of a 

 resinous lustre, and sub-conchoidal fracture; it contains more 

 water than the rocks with which associated ; and its pecu- 

 liar vitreous state may have arisen from rapid cooling, 

 through the sudden accession of water. 



4. Amygdaloid porphyry occurs near to the junction of 

 the igneous with the stratified rocks in the Ridlees burn on 

 the east side of the range. Through a felspathic base, accom- 

 panied with green earth, are scattered round chalcedonies 

 about the size of a pea and less, and also larger nodules of 

 agates and jaspers ; and, besides these, there are geodes or 

 cavities partly filled with well formed crystals of quartz. 



II. Syenite, next to porphyrite and dolerite, is the most 

 abundant rock in the Cheviots. It is entirely crystalline and 

 usually composed of red orthoclase, black hornblende, with a 

 small but variable quantity of white quartz; it occurs at 

 Housey Crag, Cheviot, Langleehope, Akeld, Yevering, Reav- 

 eley, Linhope, Standrop, Blindburn, &c. Occasionally it 

 passes into a variety of granite by the addition of mica which 

 is either silvery, yellow, or black. Specimens have been sent 

 to me with yellow shining mica as gold found in the Che- 

 viots. 



These porphyritic and syenitic hills are not rich in miner- 

 als. In cavities and veins of the rock in Hawsen burn, on 

 the north side of Cheviot, there are quartz crystals, some of 

 which are two inches long, being six-sided prisms terminated 

 by six-sided pyramids ; usually, however, the crystals are 

 small and simple pyramids. A few are amethystine, coloured 

 violet by oxide of manganese ; others are various shades of 

 brown ; and many more are white, or transparent ; and hence, 

 from their brilliancy, the locality has obtained the name of 

 the Diamond burn. Similar crystals occur on Coldburnlaw 

 and in other places. Quartz rock appears in Hawsen burn, 

 and also in considerable masses at Cat Crag, near Yetholm. 

 Green earth, in small nodules and specks, gives a varied 

 colouring to all the kinds of porphyry and syenite ; it has, 

 sometimes, been mistaken for carbonate of copper. Sulphate 

 of harytes occurs amid quartz rock and decomposing felspar at 

 Tod Crag, near Yetholm. Hematite has been seen in a vein 



