Vol. 68.] 



IN THE ' PERMIAN KOCKS OE HAMSTEAD. 



647 



I 



C^. The Eock-Farm Conglomerate Sub-group (5 feet). — 

 This sub-group, which receives its name from Eock Farm near the 

 Quarry, is seen to be about 5 feet thick in the 'New Quarry itself. 

 It is there a pronounced conglomerate, with well-rounded and 

 sometimes discoidal pebbles. It rests upon an uneven and denuded 

 surface of the strata of the underlying sub-group, and where these 

 have been most deeply eroded, the conglomerate attains its greatest 

 thickness. The pebbles are mainly limestones (Silurian and Car- 

 boniferous), usually pink or yellow in colour, but there are also 

 pebbles of yellow and red Carboniferous chert, grey quartzite, 

 vein-quartz, grits of Carboniferous type, and hornstone. 



C^. The Old-Quarry Sandstone Sub-group (20 feet). — 

 Above the conglomerate just described a massive sandstone is seen 

 in the J^ew Quarry at its northern end. The same sandstone is 

 more fully exposed in the Old Quarry, somewhat farther east, and 

 may therefore be conveniently denominated the ' Old Quarry Sand- 

 stone.' Its lower layers make a good building-stone. They are 

 hard calcareous sandstones, with chips of yellow and red limestone 



Fig. 3. — Horizontal section from Hamstead Colliery eastwards 

 to the Trias. 



New Old 



Quarry Quarry 



[Scales, Borizontal: 1 inch = 720 feet; VertiOal: 1 inch = 1410 feet.] 



and chert. Upwards they pass into thinly-bedded softer sandstones. 

 The thickness of this group is about 20 feet. 



From the Old Quarry the succession is continued along 

 the canal-cutting and along Eocky Lane. Its details are as 

 follows : — 



D,. The Manor-House Breccia and Sandstone Sub- 

 group (10 feet). — In this group are a number of thin beds of 

 breccia and brecciated sandstones, alternating with layers of 

 pebbleless sandstone. The following is the ascending order of the 

 strata, jN"o. 1 being the lowest : — 



1. Brecciated sandstones — coarse above and below, 10 feet. 



2. Flaggy sandstones, without pebbles, 4 feet. 



3. Brecciated sandstone, with two bands of coarse angular fragments 



7 feet. 



