22 



Dlt. STAMP AND MB. WOOLDRIDGE 0>~ THE [vol. lxxix, 



lower beds of these Upper Ashes. Scattered about the summit 

 and eastern slopes one sees numerous flat-topped crags, rising above 

 the general slope like crumbling castles : these are remnants of 

 the middle and upper beds of the Upper Ashes. Such masses- 

 may be seen at the points H & J marked on the map (PI. II).. 

 The Upper Ashes (excluding the higher beds described below) 

 consist for the greater part of coarse ashes, in places almost a. 

 breccia. They may be dark, but frequently are a dirty white : 

 this seems to be due to agencies other than weathering. The 

 coarse ashes are not well developed in the northern part of the 

 area, and their place is taken by fine ashes or by ' hornstones.' 



The coarse ashes pass upwards into a conspicuously-banded rock, 

 which consists of fine ashy material. Occasionally one may find 

 little bombs — an inch or so in diameter — which have dropped into 

 the soft ashy bed, and caused a puckering of the otherwise event 

 layers. This rock has been quarried in several places for local' 

 building-stone. It may be massive ; but it is more often cleaved,, 

 and splits easily into slabs about half an inch thick. 



In the upper part of these banded ashes — which are about 12 to- 

 14 feet thick — bands of hard black shale occur. The latter have 

 yielded fairly numerous graptolites, including the following : — 



Dendroid graptolites. 

 Dicellograptus sextans Hall. 

 Dicellogmptus sextans var. exilis 

 Elles & Wood. 



Glyptograptus teretiusculus var. 

 siccatus Elles & Wood. 



The graptolitic horizon may properly be regarded as occurring 

 in the highest part of the Upper Ashes, for it is succeeded by a 

 thin band of ashes, and then by the great mass of slates. 



Although only one of the species just mentioned is found also 

 at the lower f ossiliferous horizon, the two faunas may be considered 

 together, as the species occur in association and are characteristic 

 of a single horizon elsewhere. The list from the two horizons : 

 namely, just below the spilites and at the top of the Upper Ashes, 

 includes the following species : — 



Dicranograptus rectus Hopkinson. 



Dicellograptus sextans Hall. 



Dicellograptus sextans var. exilis 

 Elles & Wood. 



Climacograptus scluirenbergi Lap- 

 worth. 



Amplexograptus perexcavatus Lap-. 



worth. 

 Glyptograptus teretixisculus var. 



siccatus Elles & Wood. 

 Siphonotreta micula M'Coy. 



Miss Gr. L. Elles remarks that this assemblage is characteristic 

 of the higher part of the Grlenkiln Shales of Scotland — the zone of 

 Dicranograptus rectus. If one studies the faunas of the Dicrano- 

 graptus Shales of South Wales, it is found that three divisions, 

 can be separated: the lower one of the Hendre Shales, the middle 

 one of the Mydrim Limestone, and the upper one of the Mydrim 

 Shales. 1 The officers of the Geological Survey enumerate twelve 



1 ' The Geology of the South Wales Coalfield, pt. xi : The Country around 

 Haverfordwest ' Mem. Geol. Surv. 1914, p. 37. 



