My life : a record of events and opinions - Wallace-online.org

—RESIDENCE IN SOUTH WALES 91every heavy rain washes down earth from the ridge,while the gentler showers and mists penetrate the soilto the rock surface, which they slowly decompose.Thus, year by year, the flat portion of the summitsbecomes smaller, and a few thousand years will probablysuffice to eat them away altogether, and leaverocky peaks more like that of Snowdon. The formation,as we now find it, is, in my experience, uniquethat is, a mountain-top presenting two small patchesof almost level ground, evidently being the last remnantof the great rolling plateau, out of which thewhole range has been excavated. Double-headedmountains are by no means uncommon, but they areusually peaked or irregular, and carved out of inclinedor twisted strata. The peculiarity of the Beaconsconsists in the strata being nearly horizontal andundisturbed, while the rock formation is not such asusually to break away into vertical precipices. Theoriginal surface must have had a very easy slope,while there were no meteorological conditions leadingto great inequalities of weathering. The thick coveringof peat has also aided in the result by preservingthe original surface from being scored into gullies, andthus more rapidly denuded.After we had completed most of our work atTrallong we had to go further up the valley toDevynock. This is an enormous parish of more thantwenty thousand acres, divided into four townships orchapelries, the two eastern of which, Maescar andSenni, we had to survey. In these mountain districts,however, we only surveyed those small portions wherethe new roads or new inclosures had been made, theolder maps being accepted as sufficiently accurate forthe large uninclosed areas of mountain land. We