Читать книгу Natural History in the Highlands and Islands - F. Darling Fraser - Страница 15

SOUTH of Skye the coasts of the West Highlands fan out much more than to the north of that island. Indeed, there are several considerable islands reaching out into the Atlantic. The Outer Hebrides are not masking the influence of the Atlantic on this area as they do on the north coast of Skye. The influence of the Atlantic Ocean on this zone is both direct and inhibitory, and indirect and encouraging to a wealth of plant growth. The island of Islay, for example, changes character completely between its western and eastern halves. On the Atlantic side there is the lack of trees and shrubs and the presence of short sweet herbage salted by the spray from innumerable south-westerly gales, whereas there are beautiful gardens, palm trees and some forestry on the south and east sides. The Rhinns of Islay on the Atlantic coast are not heavily covered with peat as is a good deal of the eastern half. Islay is an island of many good arable farms, and it has several square miles of limestone country.

The waters of the North Atlantic Drift cast up on these Atlantic shores pieces of wood and beans of West Indian origin, and plants such as the pale butterwort (Pinguicula lusitanica), pygmy rush (Juncus pygmaeus) and the moss Myurium Hebridorum which occur again on British coasts only in the south-west, here turn up in fair numbers. The pale butterwort occurs in the bogs of Portugal and western Spain, and on the west coast of France; Myurium moss is found in the Azores, the Canaries and St. Helena as well as in our Outer Isles. Dwarf cicendia (Cicendia pusilla) has also turned up in this zone, though previously found in the British Isles only in the Channel Islands. More recently, Campbell and Wilmott (1946) have found another Lusitanian plant in Stornoway Castle park, namely Sibthorpia europaea. The work of Professor Heslop Harrison and his group from the University of Durham should be consulted. It is his opinion that these western cliff edges escaped the last glaciation and thus their Pleistocene flora was not exterminated. Others hold that the flora must have been introduced since then.

Jura is not so well served with the rich quality of vegetation we may find in Islay or even in small Colonsay and in Mull. It is composed of quartzite, which is poor stuff. Jura is also heavily covered with peat and suffers in consequence. A thick blanket of peat has a very great depressing effect on the variety of vegetation and in limiting the growth of deciduous trees. Jura is an island of high hills. The Paps rise to 2,571 feet and are quite rough going. It was on these hills that Dr. Walker of Edinburgh in 1812 conducted his classic experiment on the differential boiling-point of water at sea level and at the top of the Paps. Jura has a very small population of human beings on its nearly 90,000 acres. The island is so poor that its long history of being a deer forest will probably continue. In mythological literature Jura appears as being uninhabited and a place where heroes went a-hunting. It was on Jura during the latter part of the 19th century that Henry Evans conducted careful studies on the red deer. His were the first researches of a scientific character on Scottish red deer, yet he never set out to be more than a scientific amateur.

The island of Scarba, of about 4,500 acres, high and rocky, lies north of Jura. The Gulf of Corrievreckan is in the narrow sound between the two islands. This celebrated whirlpool and overfalls is caused by the strong tide from the Atlantic being funnelled through a strait, the floor of which is extremely uneven. The sound is quiet at the slack of the tide but is dangerous to small craft when the tide is running. The largest whirlpool is on the Scarba side of the sound, but there is a spectacular backwash on to the Jura coast which used to be reckoned very dangerous in the days of sailing boats. The maximum current is probably about 8¹/₂ knots which is very fast for a large bulk of water. No herring drifter or ordinary motor fishing-boat could hope to make headway against such a current, for their maximum speed in calm water is not more than 10 knots.

This West Highland zone has what the North Minch lacks, a number of sizable islands which are not big enough to lose their oceanic quality, and not so small that they are utterly windswept. The islands of Colonsay and Oronsay, west of Jura, are an excellent example of islands which have the best of almost all worlds. Naturalists may be glad that Colonsay is in the possession of one who recognizes its value and beauty in the natural history of the West. Most of the island is of Torridonian sandstone of a different complex from that farther north, but there are overlays here and there of limestone and its derivative soil, and the 100-foot beaches are another place of good soil. There are sand dunes, cliffs and rocky beaches where several rare maritime plants are to be found. There are fresh-water lochs with water lilies and the royal fern in profusion. Natural woods of birch, oak, aspen, rowan, hazel, willow and holly also occur, and beech has been planted. The sight of these, so near the Atlantic and its gales, may be imagined from this short passage from Loder’s exhaustive book:

“The woods are being rejuvenated by young plantations of Birch and Aspen, which are springing up naturally and contending for supremacy with an annual luxuriant growth of bracken. The Woodbine twines over the trees, and festoons along the edges of the numerous rocky gullies that cut up these slopes. Ivy has climbed up and formed pretty evergreens of the more stunted of the forest trees. The Prickly-Toothed Buckler Fern grows in profusion, and the little Filmy Fern is also to be seen under mossy banks.”

There has been considerable planting of coniferous and deciduous trees for amenity in this Atlantic island so that it now presents a luxuriant and well-wooded aspect in the neighbourhood of the house. But in gazing on these woods now and noting Colonsay’s wealth of small birds, we should remember the effort entailed in beginning to establish these conditions. Loder says:

“When planting in the island first began, the trees made so little headway that it was considered amply satisfactory if they formed good cover. For the first ten years or so they made little progress, and many places had to be planted over and over again. Protection from animals and weather was provided in the first instance by dry-stone dykes, 5 feet high. Alder and Sea Buckthorn were planted along the most exposed edges. Alders and various species of Poplar were used in wet situations but the poplars did not last well, and were liable to be blown over. It was only as the trees made shelter for each other that they began to show any vigorous growth. Indigenous species such as Birch, Oak and Rowan, have sprung up on hilly ground where the planted trees failed to establish themselves.”

The trunks of trees in these Atlantic places tend to become covered with lichens such as Parmelia perlata and Usnea barbata, and mosses such as Eurhynchium myosucoides (on birch), Ulota phyllantha, Hypnum cupressiforme and Brachythecium rutabulum. These trees seem to be much more affected by the humid climate than such exotics as Escallonia, Ceanothus, Verbena and Mimosa (Acacia) which grow luxuriantly. This is one aspect of Colonsay, but there are also its sedgy and heathery moors like those of many another island of the West, and at the southern tip, where the Atlantic has full play over the Torridonian and mudstone slabs gently rising from the sea to make platforms and pools near the tide level, the Atlantic grey seal breeds in fair numbers. Elsewhere, on the cliffs, kittiwakes, razorbills and guillemots breed; and there are three species of tern, arctic, common and little, breeding on the island.

Colonsay and Oronsay together might well be looked upon as an epitome of the West Highland world in its full range and consequences of Atlantic exposure and sheltered mildness.

Farther to the north-west are Coll and Tiree, two more islands which receive practically the full force of the Atlantic, but which show decided differences in natural history. Tiree is very low indeed. The rocky portion of the island, of Lewisian gneiss, reaches its highest point in Ben Hynish, 460 feet, but by far the greater part of Tiree (Plate 25) is but a few feet above sea level and composed of blown shell sand resting on a platform of gneiss. The island is one of good-sized arable crofts and is so far different from most West Highland districts that it has a Clydesdale horse-breeding society of its own. The sandy pastures of Tiree are deficient in cobalt but recent researches in mineral nutrition of animals have allowed the farmers of Tiree to dress the land with as little as 2 lbs. an acre of a cobalt salt and prevent the onset of pine in sheep. The island has particular interest for the birdwatcher: first, it is on a migration route and gets both summer and winter visitors which would not be seen anywhere in the North Minch, and its rich arable land also attracts a large number and variety of birds. Loch Vasapol of Tiree is a famous place for various duck. Tufted duck breed there and the gadwall is found there in winter though so uncommon elsewhere in the West. The vast beaches encourage certain waders, including the bar-tailed godwit, sanderling and greenshank. In the past the snipe-shooting was reckoned the best in Europe. Happily, there is less of it now.

Glacial action in Tiree is shown by the Ringing Stone, a huge rounded boulder of augite which probably came to rest there after a journey in the ice from Rum. The stone is marked by many ringed hollows on its surface.

The island of Coll, once one is within it, reminds one of the low gneiss country of Sutherland. Here the innumerable little hills are still smaller than in Sutherland and not so steep, none rising above 339 feet. The island presents a uniform rocky appearance when seen from a distance on the east side. On the west side of Coll are miles of shell-sand dunes, a feature which tends to be characteristic of many of the islands which meet the full force of the Atlantic and are low enough to have allowed the sand preliminary lodgment. The interior of Coll is just peat where it is not bare gneiss, yet with its western pastures it has always had the reputation of being a good place for cheese and sound dairy cattle. This island is important for the student, of distribution of plants in relation to the last glaciation and associated changed ocean levels.

The low, sandy islet of Gunna lies between Coll and Tiree. It is a great place for Sandwich, common and arctic terns and I believe the little tern nests there too. Such burrowers as the sheld-duck are plentiful, of course. Barnacle and grey lag geese are common in winter.

The small group of tertiary basalt islands known as the Treshnish Isles lie between Coll and Mull. The most southerly one has a rounded cone of an old volcano, 284 feet high, which gives the island the name of Dutchman’s Cap (Plate Va). The middle island of the group, Lunga, also has a volcanic mound rising to 337 feet, but the other small islands are all flat-topped with sheer sides of amorphous basalt resting on a platform of lava. This platform is of great importance in the natural history of the Inner Hebrides because it makes a breeding ground for the Atlantic grey seal. The Treshnish group, especially the Harp Rock of Lunga (Plate XIXa), is a nesting place of kittiwakes and auks and fulmars. Storm petrels nest in the Treshnish also, and the Manx shearwater on Lunga at least. The quality of grass on these islands is excellent and attracts a vast flock of barnacle geese in winter. The green rich grass of the islands is reflected again in the presence of large mixed flocks of starlings and peewits. In winter-time hundreds of blackbirds and a good many thrushes live on the Treshnish group. Lunga, being infested with thousands of rabbits, has a stock of seven buzzards.

The Cruachan of Lunga will be a good place to rest for a few moments and look at the topography of Mull, that very interesting member of the Inner Hebrides, Mull of the Mountains as the Gael calls it. The eye is first struck by the shapely peak of Ben More, 3,169 feet. This is the highest point reached by the tertiary basalt in Scotland. The cone itself is the result of great weathering, and the various beds of this amorphous lava are evident now in the truncated edges of the lower slopes of the hill. For sheer hard going, the descent from the summit to Loch Scridain takes a lot of beating, for the traveller is constantly having to make his way round these faces of rock which are not readily obvious to him as he comes down the hill. The terraced quality of Mull is obvious in a large part of Loch Scridain, the terraces being exactly the same height on either side. The peninsula between Loch Scridain and Loch na Keal reaches on the north side a stretch of some miles of very fine cliffs with sweeping talus slopes at their foot. The cliffs of Balmeanach are to my mind one of the striking features of Mull. The 1,600-foot basalt cliffs have trapped the cretaceous sandstone layer beneath them. The cretaceous sandstone—the local representative of the chalk—may be found in a narrow stratum just above sea level. These cliffs are difficult to explore and remain largely unexplored. Down below, the small island of Inchkenneth, the burial place of old Scottish kings and chieftains, is also composed of low strata of this cretaceous sandstone. If there is anywhere where chimneys must have cowls it is on Inchkenneth, for the down draughts from the great cliffs in a south wind are tremendous. Slates have to be specially cemented on the roofs. Corn and hay stacks suffer badly in this abnormal situation.

The whole of the north end of Mull consists of green even terraces with occasional gullies. The islands of Ulva and Gometra are similarly terraced flat cones with occasional gullies. The ground is porous and does not form basins for freshwater lochs; peat is absent. Bracken grows rampant here; indeed, Ulva is almost a museum piece for showing what luxuriant growth bracken can make in the Highlands. On the terraces, only the tips of the horns of Highland cattle can be seen above the fronds, but in the gullies the bracken tries to reach the same height as the plants on the terraces and may grow to a height of 12–15 feet. Trees of many kinds grow well in the sheltered parts of Mull on this soil from the volcanic rock. Just as trees were impossible on the tertiary basalt cliffs of Balmeanach and on Inchkenneth, they reach extraordinary luxuriance and beauty where the calcareous cretaceous sandstone appears again round the edge of Carsaig Bay on the south coast of Mull. This pocket will well repay a visit from the botanist and, I should imagine, from the entomologist. The cliffs to the west of Carsaig are by no means as impressive as at Gribun, but in their face there is to be seen a fine fossil tree fern first brought to the notice of geologists and naturalists by Dr. Macculloch in the early 19th century (Macculloch, 1824). Delicately coloured crystals are also to be found in these cliffs of the south coast.

The south-east end of Mull is dominated by bosses of gabbro called Sgurr Bhuidhe and Creach Bheinn (2,352 and 2,344 feet). From them we may look down on the north side to the long, bare, impressive valley of Glen More and on the south to the tree-lined waters of Loch Uisge and Loch Spelve. The southern peninsula of Laggan, formed by Loch Buie and Loch Spelve and almost made an island by Loch Uisge, reaches nowhere to more than 1,250 feet, but it is extremely rough and rocky, with plenty of scrub birch. Few people have walked through that ground which for many years now has been kept as a small and very private deer forest of 5,000 acres.

The islands of Muck and Canna are both of tertiary basalt on an erosion platform at tide level of lava that looks like clinker. Their soil is so good and their position in the Atlantic so favoured that these islands can grow what are probably the earliest potatoes in Scotland, i.e., May 31. The sheep of these islands do extremely well and come to the mainland in such good order that mainland buyers are hesitant to buy the lambs because they know they have nothing so good to offer them to keep them growing. The wealth of species of insects, molluscs and other invertebrates on these tertiary basalt islands is much greater than would be found on those of the Torridonian or gneiss formations, even though the basalt does not tend to allow lochans to form. The Glasgow University Expedition to Canna in 1936 published a full report of their extensive finds. Muck and Canna both offer the right kind of cliffs for sea birds, and Canna is also a breeding station for the Manx shearwater.

The island of Eigg (Plate 5) is a big shearwater station, the birds nesting well up towards the Sgurr, 1,280 feet. The Sgurr is the most obvious physical feature of Eigg and by far the island’s most interesting natural phenomenon. It is a geological curiosity which has shed light on the geology of other areas far distant. The late Sir Archibald Geikie solved the riddle which Hugh Miller answered unknowingly at an earlier date. The Sgurr itself is of pitchstone, resting on a thin river bed of conglomerate which contains fossil pieces of driftwood from some far distant time. Beneath this is the tertiary basalt again. The pitchstone shows columnar jointing in places, a character which is still more strongly marked on Oidhsgeir, 18 miles away to WNW. This low islet of pitchstone is considered to be part of the same sheet as the Sgurr of Eigg. There is one other feature of Eigg deriving from its geology which should be mentioned here—the musical sands of Camus Sgiotag, a small bay on the north side of the island. These sands are of partially rounded quartz grains of similar size. If the sand is dry a shrill sound is heard as one walks over it.

To return for a moment to the few acres of Oidhsgeir, an islet which does not reach higher than 38 feet above sea level. Here on the top of the pitchstone columns which are 8 inches or so across the top are found the nests of kittiwakes in the season. There are also great numbers of common and arctic terns and eider ducks. Harvie-Brown, visiting the islet several times in the ’80’s and early ’90’s of last century found teal breeding and was convinced that the pintail duck had nested there also. This phenomenon of a small islet in the open sea gathering to it an immense number of living things for the purpose of their reproduction is one to which we shall return in a later chapter on the oceanic island. The deep-cut channels among the pitchstone columns are also a playground for the Atlantic seal. One channel on the south side runs up into a pool where a boat may lie in perfect safety. Many are the occasions when lobster fishers and venturers in small boats have been glad of the quiet pool of Oidhsgeir. What a strange feeling it is to be lying snug in such a place with the mighty ocean pounding but a few yards away and the spray flying over!

The island of Rum, with its three rock types of gabbro, Torridonian and granite, is for the most part a closed book to naturalists. We may hope this unfortunate period of its history is drawing to a close and that it may yet have a future as a priceless wild-life reserve. There are red deer and wild cats on Rum, there are otters round the shores and on the burns, and such species as badgers and roe deer could be introduced if introductions were thought desirable. Some of the finest kittiwake cliffs in the kingdom are to be seen on Rum, and the Manx shearwater nests in holes high up the 2,600-foot hills. The golden eagle is there still, though the sea eagle disappeared during the second half of the 19th century. Given the chance, we may expect the chough to return to Rum.

Skye may be looked upon as the northern outpost of the Lusitanian zone. It has suffered human depopulation like many another Highland area, but Skye is still one of the most heavily crofted areas of the West. Preservation of game has practically ceased and almost all the hill ground is now crofters’ grazing. Topographically, Skye is magnificent, with its Cuillins and its Quirang, but from the point of view of wild life it is somewhat disappointing. The whole area facing the Minch is faunistically poor, as was pointed out by Harvie-Brown fifty years ago.

The island of Raasay, however, between Skye and the mainland, has a surprisingly rich variety of small birds, doubtless as a result of the woods and the large amount of park-like ground which is of Liassic origin. Personally, I should say that the Lepidoptera of Skye and Raasay would repay close scrutiny, not only from the point of view of numbers of species, but from the areas of distribution. Heslop Harrison and his group have already made fruitful researches in this direction. Raasay, like Mull, has its own sub-species of bank vole (Clethrionomys = Evotymys).

The islands of the Atlantic zone are by far the most interesting part. The mainland coasts are often hidden and tend to lose character. But the country bordering the long sea lochs is of exceptional beauty and contains some habitats—such as the indigenous oak woods—which are almost unique in Scottish natural history. To walk the length of Loch Sunart, ten miles out of the twenty through these oak woods, in the fine weather of June is an aesthetic experience, if only for the sight of the redstarts which are here in great numbers. The scenery of the distance is as beautiful as the redstart among the oaks and hazels near at hand. Perhaps the better way is to travel eastwards from Kilchoan and Ardnamurchan Point where the quality of ocean is apparent as on the islands. Sanna Bay on the northward tip of Ardnamurchan is one of the most beautiful shell-sand bays of the West, but it is rarely visited because of its remoteness. East of Glenborrodale the sense of sea is lost and we are in the woods with the loch below us. The peak of Ben Resipol, 2,777 feet, dominates the landscape and is most shapely when seen from this airt. The traveller can hardly miss seeing Ben Iadain, 1,873 feet, and on the other side of the loch in Morvern. It is a little cap of tertiary basalt perched on the Moine schist, but between the two is a very narrow band of chalk. The sight of this little hill cannot fail to impress one with the immense amount of denudation which must have taken place to remove this molten layer of amorphous volcanic rock from so much of this countryside.

Though the oceanic birds such as kittiwakes and auks are lost as one moves up these long sea lochs, it is surprising how many sea birds are to be found breeding in the season. Arctic terns, eider ducks, herring gulls and mergansers—all are here in numbers. And where there are shallow shores and estuaries there are parties of curlews, oystercatchers and ringed plovers. The hillsides above these long sea lochs are almost devoid of heather. The vegetational complex is one of various species of sedge, a few grasses such as flying bent and mat grass, and bog myrtle and deer’s hair sedge. Heather will appear at the edge of a gulley perhaps where the drainage is good. From a distance the most obvious plant may be bracken—great sheets of it, darker green in summer than the herbage and red in winter.

The ecology of the long sea lochs and their intertidal zones is a subject of great interest for those who have the techniques to follow such studies. The gradual increase in salinity from head to foot of the loch, the diurnal variation caused by the tide, the spasmodic variations caused by spates and droughts, the currents formed, and their effects on the life of the waters, still remain to be worked out in detail. Space will not allow of individual description of all the narrow and long sea lochs from Loch Fyne to Loch Alsh: each one has its similarities and distinctions, and certainly each should be visited by the naturalist who is also keen on good country. Most of these narrow lochs have high hills rising from their shores, which means that their south side loses the sun for four months in late autumn and winter. Loch Hourn is particularly sombre in winter because the hills of Knoydart, which reach to 3,343 feet, seem to tower above the loch. Loch Nevis, on the other hand, is sheltered from the north by these same hills, and the North Morar hills to the south of this wider loch do not rise above 1,480 feet. Inverie, therefore, in its sheltered bay on the north side of Loch Nevis, is one of the kindest places in the West Highlands, despite the high rainfall. Indeed, the West Coast is full of these pockets of kindly shelter allowing luxuriant growth. Many of the policies of the large houses have magnificent specimen trees which have grown within a hundred years or so to a size which would have been impossible in a large part of England.

When these sea lochs narrow at their mouth there is a diurnal tide race of considerable force. That at the Corran Narrows of Loch Linnhe runs at 8 knots at ebb and flow, but that at Connel Ferry on Loch Etive is very much more than this and is quite impassable at half tide. When the tide begins to flow here there is the extraordinary sight of a waterfall in reverse, made by the inrush of sea water.

This section may be concluded with mention of the fine piece of country round the shores of Loch Etive (Plate Vb) and up to Glen Coe (Plate 6). Ben Cruachan, 3,680 feet, is one of the landmarks of the Highlands. Cruachan and Ben Starav, 3,541 feet, are of granite and lie either side of Glen Kinglass which runs from the east bank of Loch Etive. There is happily no road through this glen and it is therefore almost untouched. The sides are lightly wooded; the river is of that clarity which is common in waters coming off granite, and as one climbs past the trees and by numerous falls the Forest of Blackmount is reached. This great high place has lost all western character which was expressed at the foot of Glen Kinglass. Blackmount has always been deer forest. Its swan song is that charming book by the late Marchioness of Breadalbane, The High Tops of Blackmount. You may object to all that this great lady stood for, but if you have a fine taste for country and appreciate writing which conveys the atmosphere of particular country you should read her book.

If one makes a cross-country trek from the heart of Blackmount to the head of Glen Etive, a country of high, spiry peaks is reached. What is more, it belongs to the nation. The Royal Forest of Dalness, Buachaille Etive, Bidean nam Bian, and some of the best climbing ground in Scotland is included, and it is probable that adjacent areas will also come under state ownership before long. The botanical and geological interest of the area is considerable, but the student of animal life will find it rather bare. Once more, at the head of Glen Coe we are on the border of our zone. As we look eastwards across the dreich Moor of Rannoch (Plate VIa) it is into Central Highland country.