NOTES AND ABSTRACTS. 



I8l 



In both old and new dunes the sand consists mainly of quartz, 

 which with orthoclase and " Kalkspat " groups forms 95 per cent. 

 The particles are chiefly from J to J a millimetre in size. The old 

 dunes are very poor in lime. 



The very youngest dunes {Triticum) contain many shells and but 

 very Httle humus : the soil is porous and often in movement. When 

 mosses and lichens fix the surface, there is no longer the same violent 

 fluctuation in temperature and water contents. So humus can 

 accumulate and a fairly luxuriant vegetation can establish itself. 



On dunes of this kind, especially where Rest harrow is abundant, 

 a crop can be raised. 



But anything which interrupts the vegetation covering can start 

 the movement of the dune, for the wind gets at any bare places. 

 Fields when abandoned, people gathering sticks, or even rabbit holes, 

 may in this way start the movement of the dune. 



There is an extraordinary variation in the conditions at various 

 points on a dune. The author gives charts and tables showing 

 differences in temperature. With an air temperature (at 1*50 m.) 

 of 15° C, the south slope was 39° and the north 17°. Then with air 

 temperature of 16 J° C, sand was 22° and grass 25°. Dew is heaviest 

 on the tops and in the windswept sandy places. Hollows in the 

 dunes are apparently sinks into which the cold air flows, so that 

 late frosts at night kill young oak leaves in a hollow whilst those on 

 the dunes above are uninjured. 



These differences are manifested by the plant covering. On 

 north-west slopes there may be thick tufts of Polypodium vulgare 

 and Botrychium, whilst on the south-east of the same dune there is 

 an open flora of Hippophae, Rubus caesius, Rosa pimpinellifolia, 

 Ammophila, and Festuca rubra arenaria. Seedling trees also occur in 

 the dune valleys and on the north-west slopes. 



But in the older dunes the Hme has been almost wholly washed 

 out of the soil, especially during the wet period which followed on 

 their formation. Not only lime but other salts are carried down- 

 wards, and may be lost in the water-table. 



But in certain places, the water rising from the underground 

 water-table meets the rain-water percolating downwards, and a sort 

 of hardpan (ortsiein) is formed which is impervious. Such places 

 may become pools in winter and quite dry in summer, or may form 

 peaty hollows. 



It is for the above reason that the older dunes do not yield a 

 satisfactory return when cultivated, even if manured, and trees grow 

 very slowly on them. Most of them seem to be overgrown by 

 Calluna or by bracken, which is apparently sometimes 9 feet in height 

 when more or less sheltered and with water at 2 feet depth. The 

 present flora is mostly a xerophytic heath flora, which is alone able 

 to establish itself under such conditions. 



The rain-water in the dune area sometimes remains fresh, floating, 

 so to speak, in the soil above the sea- water. 



