FIELD MEETINGS, 1952 
45 
t'liK’i'gos Itoiii a ]jcat bog. 'I'lio bryologists spent a profitable boiir 
exaiuiiiing tlie \egetatioii of calcareous iiiHowiiig springs from the lime- 
stone above and the acid-loving associations on the peat itself. 
Thiiradat/, 24th July. 
Pen Cerig Calcli (2502 ft.) is a prominent hill in the southern part 
of the Black Mountains, two miles due north of ( 'rickhowell. Its name, 
meaning "Limestone Summit”, is appropi iate, since the capping of the 
mountain consists of an outlier of the Carboniferous limestone as an 
island in the Old Red Sandstone, .separated from the nearest rocks of 
the same period by 4 miles. The lime, stone band on Pen Cerig (5ilcli 
repre.sents the highest point at which Carboniferous deposits ocmir in 
South Wales (c. 2200 ft.). 
The Black Mountains, having undergone extensive submarine pene- 
planation during Mesozoic times, aie really one plateau of concoidant 
heights (c. 20(H) ft.) from which deep valleys have been gouged out by 
the action of water and ice. Accordingly, the a.scent of Pen Cciig 
Call'll is at first extremely steep, but at about 1800 ft. the slope dimin- 
ishes quite suddenly. Up to the l(XX) ft. contour, the land is cultivated. 
The next 300 ft. or so of steep hillside is occupied by Pteridium , which 
has wrested complete dominance from the former bent-fescue grassland, 
which, however, still persists in less vigorous condition beneath the 
fern. At about 1600 ft. the bracken cea.ses and bent-fescue extends 
uninterruptedly to the brow of the slope. True moorland dominates 
the dome of Pen Cerig Calcli. The transition is fairly sharp from bent- 
fescue through admixture with Vaccinium. iiiyrtillus and Nardiis to a di'.y 
mooi'land dominated by Varciniuui myrtilhia, V. vitis-idnea, Knipcfrinn , 
('(diuiui and locally, on deeper peat, by Erinphorum vdy lnatv w . The 
summit is rocky and barren except for sparse wimberry. The limestone 
outcrop on the south and east sides is indicated only by the ab.sence of 
moorland species along the band and its replacement by fe.scue-dominated 
gi assland, and, where springs occur, by rushes and moss-patches contain- 
ing many typical calcicoles. On the north and west side the limestone 
forms a shallow escaiqiinent (c. 20 ft. high) in the shelter of which a num- 
ber of alpine calcicoles are preserved. The bright-green, well-grazed turf 
of fescue with TidfoVtum- spp., Plaiitngn spp. and Beilis pereiinis contrasts 
sharply with the dull brown hues of the moorland on the grits and 
conglomerates of the Old Red Sandstone and Millstone Grit. 
From Pen Cerig Caleb, the party continued northwards along the 
peaty ridge to Pen Allt Mawr (2360 ft.). The vegetation on the ridge 
there is most interesting, indicating the probable sequence of events 
leading to the replacement of original Eriophorum moor on deep peat 
liy heatlier And wi:nberry on shallow sandy peat. The dominance of 
Eriophorum is undisputed on deep undisturbed peat. Erosion of peat 
and consequent drying of the surface is accompanied by invasion of the 
tussocks by Vaccinium. and of the eroded channels by Oalluno. 
The party descended on the east side into Cwm Banw, a short narrow 
valley separated by a spur of the Pen Allt Mawr ridge from the main 
