THE GEOLOGY OF ORKNEY. X¢l 
higher horizon the remains of trees, especially Betula 
verrucosa, Ehrh., and Corylus avellana, form usually 
a well-defined layer. This is the lower Forest Bed; 
temperate woodland marsh plants occur in this 
stratum. Mr Lewis gives a list of the plants identi- 
fied by him in this deposit :—Ranunculus hederaceus, 
R. Lingua, R. flammula, R. acris, R. repens, Viola 
hirta (seeds), Lychnis diurna (?) (seeds plentiful), 
Hypericum pulchrum (seeds not abundant), Montia 
fontana (seeds very abundant), Potentilla Pragara- 
astrum (a few achenes), Pyrus Aucwparia (wood and 
twigs), Arctostaphylos Uva-Ursi (one seed), Cala- 
mintha officinalis (nutlets), Ajuga reptans (nutlets), 
Myricu Gale (twigs), Alnus glutinosa (wood and 
catkins), Betula verrucosa (wood, seeds, and catkin 
scales), Carex paniculata (very abundant), Carex sp., 
Osmunda regalis (sporangia). 
A consideration of this list shows that the climate 
must have been very much more favourable than 
when the Arctic willow overspread the low grounds 
of Shetland. 
When we consider more carefully the distribution 
of the lower Forest Bed in Shetland, some remarkable 
facts come to light. The remains of well-developed 
trees are found even in the most exposed situations, 
where it is impossible to grow trees at the present 
day, even with careful artificial shelter. They occur 
near the summits of the hills in the centre of the 
Mainland, and even in the island of Foula. The 
trees do not represent copses growing in sheltered 
valleys away from the coast, but appear in every 
district hitherto visited, and are just as well devel- 
