POSTGLACIAL, &c., DEPOSITS OF CONTINENT. 485 



time districts are only feeble representatives of the arborescent 

 vegetation which in former days appears to have covered the 

 major portion of Northern Europe. Even within historical times 

 the forests are known to have been more extensive than they are 

 now, but the true Age of Forests goes back to an archaeological 

 period. 



There are three principal kinds of peat-bogs described by 

 continental writers, which correspond to our meadow-bog, hill- 

 bog, and bog with buried trees or forest-bog. 1 These different 

 kinds of bog pass into each other, so that a hard-and-fast line 

 cannot always be drawn between them. From our present 

 point of view the forest-bogs are the most important, and not 

 the least interesting are those of Denmark, described by Pro- 

 fessor Steenstrup. They are found in basins of inconsiderable 

 size, which, however, are deep in proportion to their width. 

 Some of the smaller bogs are not much more than 30 or 40 yards 

 across. The pot -like depressions which have been specially 

 examined by Steenstrup occur in the great drift or glacial de- 

 posits that cover so wide an area in Denmark, and appear to 

 have existed at one time as pools and lakelets. This is shown 

 by the appearance at the bottom of the bogs of alluvial clay and 

 marl, with remains of freshwater organisms and land -plants. 

 From this clay Nathorst, in company with Steenstrup, extracted 

 the relics of an arctic flora, consisting of polar willow (Salix 

 polaris), herbaceous willow (8. herbacea), netted-leaved willow 

 (S. reticulata), mountain - avens (Dryas octopetala), and dwarf 

 birch {Bctida nana). Immediately above the clay, in the Lille- 

 mose and other bogs of the same character, comes a layer of 

 water-plants (Potamogeton, Chara, Myriopliyllum), with leaves of 

 the aspen (Populus tremula), and this in turn is covered with a 

 stratum of peat composed of Hypnum cordifolium, and contain- 

 ing trunks of Scots fir (Pinus sylvestris). These trees had evi- 



l The Danish terms are Kjcermose or Engmose, Lyngmose, Svampmose or 

 Hoermose, and Skovmose, which answer to the German Wiesenmoor, Haidenmoor 

 or Hochmoor, and Holzmoor or Waldmoor. Many varieties of peat are described 

 by German writers, such as Sump/moor, Sumpftorf, or Moostorf (Sphagnum peat), 

 Eaidetorf 'or Erikentorf (heather-peat), M. arschtorf (marsh-turf ), etc. 



