`The very loneliest place in this country" as judged by Robert Lloyd Praeger (who, after all, had walked most of the island and should know) was the Nephinbeg hills of north Mayo and the vast apron of lowland bog surrounding them. "Where else even in Ireland," he asked in The Way That I Went, "will you find 200 square miles which is houseless and roadless - nothing but brown heather spreading as far as you can see . . ?"
Even today, with great tracts of the bogs mined or forested and the first row of wind turbines marching along the cutaway, the wild, tundra-like atmosphere of these peatlands remains - a primal core for a new national park. Far from bleak or depressing, Praeger found the loneliness "inspiriting". But, if ever he shared my own keen fantasies about this landscape, he kept quiet about them.
The last Ice Age left several parts of Ireland uncovered. Much of Munster, away from the mountains, was free of ice, together with a few bits of Connacht. This stretch of Mayo, between the Nephins and the ocean outside the Mullet peninsula, was an ice-free zone, and it still conjures for me a raw space and silence, with the ice piled up beyond the hills.
How exciting and appropriate, then, that plants now discovered at secret waterways within the bogs should be rare relic species from the ancient, post-glacial fens of Ireland - the kind of fens which supported the growth of the great raised bogs now shaved away by Bord na Mona.
This Mayo blanket of peatland is not nearly so featureless and uniform as it can seem from a distance. Praeger's talk of "nothing but brown heather" gave the wrong idea: the lowland bogs are wet and deep, shimmering with moorgrass and black bog-rush and threaded with channels, pools and lakes. They have formed in a basin of limy glacial debris, so that their margins are actually calcium-rich.
These are the places where astonishing, rare mosses are growing - plants until recently known to Irish botanists only as fossil species, their fronds unravelled from the lowest organic layer at the base of raised bogs. They belong to northern plants which were abundant in Ireland and Britain in the post-glacial Boreal period, but largely died out with the change to a warm, wet oceanic climate.
It was in the late 1950s that such a relic moss, Meesia triquetra, was found by two women botanists not far from the site of the present row of windmills at Bellacorick. It was the only living plant of the species ever seen in either island and has never been refound. But in the 1980s the lure of its rarity led Dr Neil Lockhart, now Duchas's expert on mosses and liverworts (bryophytes), to begin searching other fens in the area. He found two further relic mosses, growing with other rare northern species of higher plants (a marsh orchid, a yellow saxifrage) and began to recognise, in the iron-stained, calcium-rich pools and their quaking lawns of moss, the last remnants of fens of a post-glacial landscape.
Then, last summer, he came upon the robust and beautiful Paludella squarrosa, never found in Ireland as a living plant and extinct at its few sites in England since about 1916. An intricate folding of its leaf-tips makes each stem a baroque bracelet of woven hearts - "a most curious moss, of unbelievable appearance," as one scholarly US reference work describes it.
But its Irish significance goes far beyond mere beauty. This was one of the sturdy mosses which, growing densely at the surface of the post-glacial fens, made a transitional mattress above the mineral-rich groundwater. On top of them began the growth of sphagnum mosses, nourished entirely from rain, laying the foundations of the subsequent peat bogs.
Dr Lockhart, returning to the bogs this summer, believes the fens of north Mayo "still harbour many secrets" and worries about their security from drainage and afforestation - even, indeed, about the trampling Wellingtons of other mad-keen, camera-toting bryologists.
The post-glacial fortunes of Ireland's natural world enter, in a most lively way, The History of British Mammals, just published in the Poyser Natural History series (£30 in the UK). Its author is Dr Derek Yalden, editor of Britain's influential Mammal Review, and a long-time student of post-glacial colonisation.
Ireland, says Yalden, is big enough, and has a wide enough range of habitats, to hold a lot more species: yet there are no moles or weasels, common shrews, field voles and so on. And, in the fossil record, we miss mammals such as beaver and elk, which we easily might have had.
For our earlier fossil mammals, he turns to the new research project, led by Prof Peter Woodman, which gives firm radiocarbon dates to the bones of extinct mammals recovered from our limestone caves and bogs. Mammoth, Arctic fox and lemming, for example, were still hanging on at the height of the last glaciation; brown bears, wolves and lynx were here to greet the first people.
In any assessment of the present Irish fauna, arrival by land bridge from Britain has been an almost inescapable explanation. Yalden has contributed his share to past discussion of where the bridge might have been and when, and bravely faces up to revision. The new theory of a low-lying, transitory bridge, produced by a crustal "forebulge" and migrating slowly up the Irish Sea as the weight of ice was lifted, makes for a fascinating set of maps and conjectures.
In his intriguing final chapter, he looks at the pros and cons of reintroducing mammals to Britain, either from historical extinction (wolf, beaver) or to help recovery (otter, pine marten). His sympathy is rather more than sneaking. The wild boar, he says, "would be a magnificent presence" as well as a good rooter-out of bracken.
