90 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



thickness of at least a thousand feet, and probably somewhat 

 more. Interstratified with these shales are numerous beds of volcanic 

 ash, grit, and lava, which have a general parallelism, and a direction 

 from north-west to south-east. The harder lava-beds often form 

 oval or rounded bosses which stand out rather conspicuously from 

 the level plain. The following section, taken across the northern 

 extremity of Coal Hill, will serve to show the mode in which the 

 volcanic beds and shales are interstratified. 



These volcanic rocks differ considerably in their appearance and 

 mineral structure. The ash has generally a light-greyish and 

 greenish-grey colour, which becomes yellowish brown near the 

 surface, from peroxidation of the iron it contains, and is made up 

 for the most part of minute felspathic grains, with occasionally a few 

 scattered imperfectly formed crystals of hornblende. Some of the 

 harder and more compact varieties are of a bluish-grey colour, effer- 

 vesce with acid, and contain sometimes as much as 11 percent, of 

 carbonate of lime*. The grits are more granular, and often cellular, 

 of a brown or ohve-brown colour, and without inspection might pass 

 for sandstones ; they contain, however, no siliceous particles t. The 

 lavas are more variable in their appearance ; some of them, as the 

 one near Fowlet's Farm, are of a reddish-brown colour, amorphous, 

 and compact, extremely tough, and resemble those which occur in 

 the Hollybush Sandstones. For the most part, however, they are 

 richer in augite, and of a dull greenish colour, with disseminated 

 portions of greenish-black hornblende. In the boss at Eowick, and 

 at Coal Hill, the rock has a more trap-like ajipearance, and the 

 felspar and augite are more distinctly separated, but nevertheless 

 can scarcely be called crystallized. Like trap also, and some modern 

 lavas, the rock breaks into rectangular blocks, which, in weathering, 

 cast off concentric layers, and leave rounded balls. At Ro'^dck this 

 lava has associated with it some highly calcareous blue shale ; and 

 similar shale occurs also on the east of Coal Hill. 



The greater portion of the lava and ash-beds belonging to the 

 Elack Shales occurs between the north-west slope of the Keys End 

 Hill and the turnpike-road leading from Tewkesbury to Eastnor ; 

 but a little further to the north, below the escarpment of the May 

 Hill Sandstone, at the Obelisk near Bransill Castle, there are four 

 other bosses of similar volcanic rock. It is mostly of a dark greenish- 

 grey colour, with scattered portions of hornblende, and some cavities 

 filled with carbonate of lime. Other portions are of a blue colour, and 

 very compact, containing some carbonate of hme, but less than might 

 have been expected from its appearance ; and when this is removed by 

 an acid, the residue has the same composition as the other portions. 

 In the largest of these bosses, haviiig a httle plantation on the top 

 of it, shale is interstratified with the lava-beds J. 



* The Rev. J. H. Timins's MS. 



t They fuse readily before the blowpipe. 



X The rocks fi'om several of these bosses, as, for instance, those near Bransill 

 Castle, Fowlet's Farm, and Kowick, have been examined chemically by the 

 Rev. J. H. Timins, and the results of his analyses are pubhshed in the Edin. 

 New PhU. Journ. New Series, vol. xv. 1862, pp. 1 et seq. 



