304 CARBONIFEROUS VOLCANIC ROCKS. 



becomes nearly white, and then its constituents are completely decom- 

 posed, though the felspar is usually unaltered. The Titerston Glee 

 Hills are capped by columnar dolerite, in which the olivine is nearly 

 unaltered. A similar rock is found at Knowle Hill near Kinlet, but 

 where in contact with the sandstone on which it rests, both the augite 

 and felspar are converted into a yellow granular substance. At Whit- 

 wick colliery, where unaltered New Red Sandstone rests on dolerite, 

 most of the augite has a purple tinge. The dolerite ridge near Shat- 

 terford has the minerals altered only above the sides of fissures, and 

 in places assumes a porphyritic texture, when it abounds in grains of 

 magnetite. At Swinnertoii Park, eight miles N.E. of Stafford, the rock 

 abounds in augite and olivine, with comparatively little plagioclase. 



Diorites of Warwickshire. In the Warwickshire Coalfield diorites 

 occur in the district about two miles south of Nuneaton. The several 

 binds and masses are limited to the lower part of the coal measures, 

 which are here unproductive, and to the millstone grit. They run 

 in the planes of bedding, but are clearly intrusive, since the rock is 

 altered above and below them. They are well seen in the railway 

 cutting near Chilvers Coton. The eruption was previous to the 

 deposition of the Trias. These diorites vary a good deal in composi- 

 tion. That seen near Marston Jabet has the external appearance of 

 basalt, and contains small crystals of hornblende of a clear-brown 

 colour, lying in a matrix of triclinic felspar, with numerous grains of 

 magnetite, and a few hexagonal needles of apatite. But sometimes 

 the ground mass is a good deal altered, being converted into a sub- 

 stance like serpentine, and the felspar becomes turbid. The diorite 

 of Purley Park, near Atherstone, consists of a mass of plagioclase 

 crystals, with a few crystals of orthoclase. Crystals of brown horn- 

 blende are abundant, and crystals of yellowish augite frequent. There 

 are many pseudomorphs after olivine, usually replaced by calcite and 

 viridite. This is the only augite-diorite recorded in this country, but 

 the quantity of augite varies much in different specimens. 1 



Basalt in Arran. Much of the southern half of Arran consists 

 of sheets and masses of basalt of Carboniferous age, with intrusive 

 sheets in places. The dolerite of the Clauchland Hills extends east- 

 ward to Dunfion, and reaches the coast at Clauchland Point. A 

 similar sheet caps Ross Hill, near Lamlash. Sheets of dolerite form 

 a succession of terraces in the cliffs between Deppin and Benan Head 

 on the S.E. coast, and these three or four sheets are traced inland in 

 the beds of streamlets. The lowest sheet, seen at Kildonan Castle, has 

 the characters of an augite -andesite. On Auchenhew and Levencorroch 

 Hills the dolerite is columnar. 2 



Trees in Volcanic Ash in Arran. On the north-east coast of 

 Arran, near the base of the carboniferous series, eleven distinct beds of 

 volcanic ash occur in a distance of 400 feet, alternating with layers 

 of shale and coal, which are inclined at an angle of 37. Mr. 

 E. A. Wunsch records the occurrence of twelve or fourteen stumps of 



1 Allport: "Diorites of Warwickshire Coalfield," Q. J. G. S., vol. xxxv. p. 637. 



2 Allport : " Carboniferous Dolerites," Q. J. G. S., vol. xxx. 



