POSTGLACIAL, &c, DEPOSITS OF CONTINENT. 491 



one grows more rapidly than another." The undrained bogs of 

 Ireland would thus appear to be still increasing, which is not 

 the case generally in Scotland, although in the rainier districts 

 the evidences of arrested growth and of decay are less conspicu- 

 ous than elsewhere. The sum of the matter is that we have no 

 exact data by which to compute the time required for the for- 

 mation of a given thickness of peat, the rate of growth being 

 extremely variable, not only in different regions, but in one and 

 the same bog. Moreover, even if we could prove the present 

 existence of an uniform rate, the fact that the climate has 

 undergone considerable changes would vitiate our results, and 

 render our standard of measurement of no avail. Nevertheless, 

 in very many cases, it is quite evident that the bogs are of great 

 antiquity, and that it has often taken several thousands of years 

 to form a thickness of twenty, or even of ten, feet. Thus Steen- 

 strup thinks it may have required at least four thousand years 

 for the growth of the Danish forest-bogs, and perhaps this, he 

 says, may be only a third or fourth of the time actually involved. 

 I have mentioned the fact that an arctic flora has been 

 found at the base of the Danish forest-bogs. Mr. Nathorst has 

 detected the same flora in over twenty localities in southern 

 Sweden. 1 The most southerly place from which he has recorded 

 this interesting flora is near Greflunda and Bastekille, on the 

 borders of the parishes of Mellby and Hvitaby, where he ob- 

 tained the arctic willow in freshwater clays under a bed of 

 peat, at a height of 400 feet above the sea. The other localities 

 ranged from 150 to 500 feet above the same level. The general 

 succession of the deposits met with was as follows : — 



feet. 



Peat . 



3j to 4 



Silt . 



JtolJ 



Sand . 



to 1 



Silt with shells 



11 to 4J 



Sand . 



to 1 



Sandy clay 



21 feet. 



Sandy clay with mosses 



li » 



1 Geol. For. i Stockholm Fork., 1877, Bd. iii. No. 10. 



