80 F. Barke, Wheelton Hind, and A. Scott — 



considerable pressure. This effect is very similar to the one com- 

 monly observed in Bunter pebbles. In one specimen of the con- 

 glomerate the detrital material is mainly vein-quartz, and practically 

 every pebble shows decided traces of the effect of pressure. The 

 occurrence of this rock, with such a large proportion of vein-quartz, 

 is interesting, as bands of similar material can be observed in some 

 of the sand- and clay-pits near Friden, Derbyshire. 



In many specimens the pieces of vein-quartz, although originally 

 of a rounded form, have invariably a marginal development of 

 secondary quartz in optical continuity with the original grain, 

 and possessing perfect external crystal forms. The latter are so 

 sharply defined as to make it practically certain that the secondary 

 growth has occurred in situ, as even slight rolling would have reduced 

 to some extent the perfection of the faces. The presence of secondary 

 growths on quartz has been noticed by Howe ' in the material from 

 the Ribden Pit. 



A pebble of equigranular quartzite, with relatively large inter- 

 locking quartz crystals and little visible cementing material, has 

 a decidedly metamorphic asjDect, and is probably derived from 

 pre-Cambrian or early Palaeozoic deposits. Several types of sand- 

 stone which closely resemble some of the Carboniferous rocks of 

 the Midlands are also present. A fine-grained sandstone, which is 

 made up of subangular grains of quartz with subordinate felspar 

 in a siliceous matrix of quartz and colourless mica, is very like some 

 of the local rocks of Millstone Grit age, which have been used for 

 refractory purposes, while other rocks, which can also be matched 

 among the local deposits of the same age, included a coarse sand- 

 stone with rounded quartz crystals and scarce felspar in a cement 

 of secondary quartz, and a fine-grained siliceous conglomerate, 

 consisting of fragments of rounded vein-quartz, quartzite, sand- 

 stone, and shale in a matrix of secondary quartz and mica. These 

 rocks resemble closely the so-called " ganisters " of the Stockton 

 Brook district. 



Another rock which has angular to subangular quartz grains 

 with little or no felspar, set in a mosaic of interlocking crystals 

 of very fine secondary quartz, closely resembles some of the crow- 

 stones of the Pendleside Series which occur in the neighbourhood 

 of Congleton. Other equigranular rocks, consisting almost entirely 

 of quartz, with wavy extinction, and thin interstitial layers of cement, 

 are suggestive of the ganisters of the Lower Coal-measures. 



Several fragments referable to chert can also be recognizgd, 

 and others of very fine grain appear to be indurated quartzose 

 shales. The igneous rocks include tuffs, etc., as well as felsites 

 with a decidedly aphanitic texture. 



With regard to the proportions of the various rock-types, the 

 fragments of quartz rock far exceed the others in amount, and of 

 these the sandstones and " crowstones " preponderate over the 



1 Loc. cit., p. 146. 



