Z7^ 



NA TURE 



[August i8, 1S98 



from view. The crowded leaves have in-folded edges. There 

 are thus formed innumerable narrow chinks, in which water may 

 creep upwards. The microscope brings to light further con- 

 trivances, which answer the same purpose. Many of the cells 

 of the leaf lose their living substance, and are transformed into 

 water-holding cavities with thin, transparent walls, which are 

 prevented from collapsing by spirally wound threads. But the 

 water must not only be lodged ; it must ascend, and supply the 

 growing branches above. Accordingly the water-holding cells 

 are not closed, but pierced by many circular pores, which allow 

 liquid to pass in and out freely. Perforated water-cells also form 

 the outer layers of the stem. Thus the whole surface of the plant, 

 whether immersed or not, is overspread by a water-film, which 

 is easily replenished from below as it evaporates above. It is 

 the water-spaces which render the Sphagnum so pale. The 

 green living substance forms only a thin network, traversing the 

 water-holding tissue. 



Now and then we are lucky enough to see the bed of a Sphag- 

 num-swamp. Quarrying, or a land-slip, or the formation of a 

 new water-course, may expose a clean section. I have known 

 the mere removal of big stones, time after time, from the bed of a 



Fig. 2.— Detail of Sphagnum- leaf ; green cells with corpuscles, and water- 

 cells with spiral threads and pores. Below is a section (from Sachs) of 

 part of a leaf. 



stream fed by a Sphagnum-swamp, gradually increase the cutting- 

 power of the running water, until the swamp is not only drained, 

 but cut clean through down to the solid rock. Then we may 

 see that the peat rests upon a sheet of boulder-clay, and this 

 upon the sandstones and shales. Between the peat and the 

 boulder-clay there is sometimes found an ancient seat-earth, in 

 which are embedded the mouldering stumps of long-dead trees. 

 Oak, Scotch fir, birch, larch, hazel, alder, willow, yew and 

 mountain-ash have been met with.^ Where a great tract of 

 peaty moorland slowly wastes away, the tree-stumps may be 

 found scattered thick over the whole surface. Above the seat- 

 earth and its stumps, if these occur at all, comes the peat, say 

 from 5 to 20 feet deep, and above the peat the thin crust of 

 living heather. 



Every part of the moor has not, however, the same kind of 

 floor. Streams in flood may excavate deep channels, and wash 

 out the gravel and sand into deltas, which often occupy many acres, 

 or even several square miles. The outcrops of the sandstones 

 crumble into masses of fallen blocks. Instead of the usual im- 

 pervious bed of boulder-clay, we may get a light sub-soil. The 

 verges of the moor have commonly this character ; they are 



1 In Yorkshire I think that birch and alder are the commonest of the 

 buried trees. 



by comparison dry, well drained, and overgrown with furze, 

 bilberry, crowberry, fern, and wiry grasses ; such tracts are 

 called "roughs" or "rakes" in the north of England. A 

 similar vegetation may be found far within the moor, though not 

 in places exposed to the full force of the wind. Even on the 

 verges of the moor there are very few earthworms, and at most 

 a scanty covering of fine mould ; in the heart of the moor there 

 is no trace of either. The Nematoid worms which are so 

 common in most soils, and easily brought to the surface by pour- 

 ing a few drops of milk upon the ground, seem to be absent 

 from the moor. Insects and insect-larvae are very seldom found 

 in the humus. 



In a country where population and industry grow steadily, it 

 is rare to find the moor gaining upon the grass and woodland. 

 We have to go back some centuries to find an example on any- 

 thing like a large scale. The Earl of Cromarty {Phil. Trans. 

 No. 330, p. 296), writing in 1710, says that in 1651 he saw a 

 " firm standing wood " of dead fir-trees on a hill-side in West 

 Ross-shire. About fifteen years later he passed the same 

 spot, and found no trees, but a ''plain green moss " in their 

 place. He was told that the trees had been overturned by the 

 wind, and afterwards covered by the moss, and further that 

 none could pass over it because it would not support a man's 

 weight. The Earl "must needs try it," and fell in up to the 

 arm-pits. 



A section through a thick bed of peat will sometimes reveal 

 the manner of its growth. The lower part is often compact, the 

 upper layers of looser texture. It is not uncommon to find by 

 microscopic examination that while the lower part is made up 

 entirely of Sphagnum, the more recent growth is due to heather, 

 crowberry, grasses, hair-moss, and lichens. In some places the 

 whole thickness is of Sphagnum only ; in others there is no 

 Sphagnum at all. Peat formed of Sphagnum only has no firm 

 crust, and from the circumstances of its growth it is likely to be 

 particularly wet. Sphagnum often spreads over the surface of 

 pools or even small lakes, not nearly so often in Yorkshire, 

 however, as in a country of well-glaciated crystalline rocks, 

 where lakes abound. In such cases a peculiar kind of peat is 

 formed as a sediment at the bottom of the water, which may in 

 the end fill up the hollow altogether. A very slight cause is 

 enough to start a Sphagnum bog, such as a tree falling across a 

 stream, or a beaver-dam. When a pool forms above the dam, 

 the Sphagnum spreads into it, and the peat begins to grow. 

 Long afterwards, when the hollow is completely filled with 

 peat, there may be a chance for grasses, rushes, crowberry and 

 heather. 



In our own time and country the moors waste faster than 

 they form ; it is much commoner to find the grass gaining on the 

 heather than to find the heather gaining on the grass. There 

 is no feature of the Yorkshire hills more desolate than ground 

 covered with wasting peat. The surface is cut up by innumerable 

 channels, with peaty mounds between. These are either abso- 

 lutely bare, or thinly covered with brown grasses and sedges. 

 The dark pools which lie here and there on the flats are over- 

 hung by wasting edges of black peat. It is cheerful to step 

 from this dismal territory to ground clothed with close-growing 

 grasses of a lively green, such as we find where the peat has 

 disappeared altogether. 



The moors are commonly wet, very wet in places. In certain 

 parts and during certain seasons of the year they are, however, 

 particularly dry, and subject to a severity of drought which the 

 lower slopes and the floor of the valley know nothing of. At 

 lower levels trees give shelter from sun and wind ; night- 

 mists check evaporation, and even return a little moisture to the 

 earth ; the deep, finely divided soil lodges water, which is given 

 off little by little, and in our climate never fails to yield an 

 effective supply to the roots ; pools and streams dole out 

 sparingly the water which fell long before as rain. But the 

 moor lies fully open to sun and wind. In March it is exposed 

 to the east wind ; in June to hot sun and cold, clear nights ; in 

 August there is perhaps a long spell of drought ; in November 

 heavy gales with abundance of rain. The summer is late ; the 

 moorland grasses make little growth before the beginning of 

 June ; even then the heather bears few young leaves, while the 

 fronds of the bracken are only beginning to push through the 

 soil. Whatever the weather, there is no protection against its 

 extremes ; there is no shelter and no shade. The air is cold ; 

 wind and the diminished pressure due to height favour rapid 

 evaporation. Though the Sphagnum-patches form permanent 

 bogs, a great part of the moor becomes far drier in a hot summer 



NO. 1503, VOL. 58] 



