386 



PAST succession: the ceneosebe. 



Andersson (1895) has recorded the layers and species of a peat-bed in Gotland, 

 which lay below the highest shore-line of the sea of the Ancylus period, and is 

 now 28 m. above sea-level: 



The Dryas layer contained Salix polaris, S. arbuscula, Betula nana, Dryas, 

 Empetrum, Carex, Ardostaphyliis alpina, Myrtillus uliginosa, Potamogeton 

 filiformis, Myriophyllum spicatum, Hippuris vulgaris, Zannichellia polycarpa, 

 Amhlystegium scorpioides, A. chrysophyUum, Chara hispida, crinita, emdfoetula, 

 and Tolypella intricara. The birch layer exhibited Betula nana, B. odorata, 

 Dryas, Salix phylidfolia, Hippophae, Juniperus, Empetrum, Arctostaphylus 

 uva-^rsi, Myrtillus, Carex, Potamogeton, Chara, etc. The pine layer showed 

 Pinus silvestris, Populus tremula, Betula odoraia, Salix nigricans, Juniperus, 

 and Arctostaphylus uvorursi. The upper peat layer contained pine and birch, 

 and especially Cladium mariscus. 



Sernander (1895) has assumed a cooling of the Swedish climate during the 

 Litorina period, and consequent migration of northern species to the south: 



These again moved northward with a subsequent amelioration of the 

 climate, and, as in the case of Betula nana and B. intermedia here considered, 

 were to be found in the southern area only as relicts of the colder period. In 

 support of his conclusions, the author has made an exhaustive study of the 

 moor concerned. The vegetation about the moor consists of birch forest 

 mixed with spruce and pine, of aspen woodland with hazel, and also of scrub 

 and swampy meadow. In the moor itself the central part is occupied by 

 Sphagneta schoenolagurosa, which pass over into Sphagneta myrtillosa, and 

 these into Pineta sphagnosa mixed with birch. In the Sphagneta myrtillosa 

 occur Betula nana and B. intermedia in limited areas. The structure of the 

 moor is as follows: lowermost is found the Ldtorina clay, upon which occurs a 

 layer of fresh-water slime with numerous fossils. The slime passes over above 

 into Phragmites peat, above which Ues a stump-layer of 3 to 9 dm. in thick- 

 ness. The latter is covered by a mass of peat 4 to 8 dm. thick. In the slime 

 are foimd stems of deciduous trees which have been gnawed by the beaver. 

 Trapa natans appears here also. The spruce occurs in the stump-layer and 

 Naias marina in the Litorina clay. 



The sequence in the moor is assumed to indicate the following developmental 

 history. In the Atlantic period, the moor was a bay of the Litorina sea. 

 This bay was silted up with clay and isolated from the disappearing sea as a 

 small lake, in which Phragmites and other plants grew. Here was found 

 Trapa also. At the margin grew Carex, and behind this an alder scrub, 

 followed by a dense vegetation of Betula alba, Tilia europaea, Qu^cus robur, 

 etc. At the time of the filling of the bay, the climate became drier, and the 

 sub-boreal followed the Atlantic period. Xerophilous formations and forests 

 invaded the moor and finally the pines became the sole dominant. 



Weber (1895) has studied the upper of three beds of "brown coal" alter- 

 nating with layers of clay and sand, discovered in Holstein in 1889: 



The upper bed, of the diluvial period, consists of four layers. The fourth 

 layer shows no trace of plant remains, while the third contains pine pollen, 

 and pollen and wood fragments of the oak. This layer grades into the lowest 

 sandy portion of the peat, with which the "brown coal" bed proper begins; 

 this sandy portion contains remains of Ceratophyllum and Potamogeton, together 

 with those of oak and willows, indicating open water surrounded by these 

 trees. Then foUows a peat layer with abundant relics of swamp and water 

 plants, with many remains of oak, the first evidences of spruce, and a decrease 



