16 GENERAL HISTORICAL SUMMARY. 



and fruits of Betula. In the upper part occur pine leaves and trunks. The 

 next layer, q, is composed of Sphagnum, with Oxycoccus wlgaris, Andromeda 

 polifolia, Scirpus caespitosus, and Eriophorum angustifolium in the upper 

 portion, together with some oak and birch. This is followed by a layer u 

 of Hypnum proUferum, with remains of both oak and birch, and this is in turn 

 covered by an extensive layer of alder peat t'. 



The peat layers of the two moors not only afford a record of the successive 

 populations which occupied the basin, but also of the different forests which 

 clothed its margins. In the basin proper, Vidnesdam shows but two strata of 

 moss peat, namely, the Sphagnum and the Hypnum cordifolium layers, while 

 in Lillemose there are three strata and in the reverse order, viz, Hypnum 

 cordifolium, Sphagnum, and Hypnum proUferum. As to the margins, it is 

 assumed that the banks were without vegetation during the period in which 

 no plants had appeared in the water of the basin. With the early stages of 

 water vegetation, forest seems to have appeared on the banks, for the quantity 

 of aspen leaves foimd in layer n shows that this tree must have been dominant. 

 These give way about the middle of layer p to abundant pine needles, indicat- 

 ing that the aspens had been replaced by pine, as would be expected in the 

 normal succession. The marginal layer r testifies to the length of the period 

 for which the pine dominated the margin, but it finally yielded to the oak, as 

 is shown by the plant remains in layer q. The marginal layer s is perhaps due 

 wholly to the oak forest, but this seems to have been destroyed by increasing 

 moisture, resulting in a Hypnum layer, which was finally succeeded by Sphag- 

 num and alders. 



There is thus no doubt that these two moors have developed during a period 

 in which several forest vegetations have arisen and disappeared. The aspen 

 forests may be regarded as preparatory to the pine and oak forests, which 

 probably dominated the region for thousands of years, but have practically 

 disappeared from the country to-day. While these forests, as well as the moor 

 vegetations, belong in a definite time sequence, it is practically impossible 

 to assign any absolute time for any or all of the layers. 



The foiu" forest vegetations, viz, aspen, pine, oak, and alder, found above 

 each other in Vidnesdam and Lillemose, occvu- in all the forest moors of north 

 Sjelland, and other evidence points to their former occurrence throughout 

 Denmark. These four forests not only succeeded each other in the moors, 

 but everything points to a synchronous succession on the uplands, so that one 

 may speak of a pine period, for example, for the whole country. The final 

 alder forest of the moor was succeeded by the beech forest which is now the 

 dominant one. However, no trace of the beech has been found in the moors. 

 Thus there seems no doubt that one vegetation succeeded another in such a 

 way that the latter grew on the ruins of the former, and that the replacement 

 of one by the other was the result of a slow natural cycle. In this cycle one 

 organization develops and then gradually calls forth conditions which cause 

 its disappearance and hasten the development of a new organization. 



Reissek, 1856. — Reissek (1856:622) studied in detail the formation and 

 succession of islands in the Danube. These arose through separation from 

 the mainland, or through the deposition of gravel and sand. It was thought 

 that islands due to deposition were laid down irregularly and without sorting, 

 and that their formation bore no direct relation to the development of vege- 

 tation. The author found the process of formation both definite and regular, 

 and the influence of the vegetation fundamental. Each island was at first a 

 sand-bar due to high water or ice action. The first vegetation consisted of 



