GENERAL VIEWS ON ARCHAEOLOGY. 307 



ance gave place to others ; the hog-moss, {Sphagnum,) and finally the 

 heather made its appearance. Firstly came the cranberry, (Vaccinium 

 oxycoccos, L.,) the Vaccinium uliginosum, (L.,) and the Erica tetralix, 

 (L.,) and lastly the Erica vulgaris, (L.) The arborescent vegetation 

 of the pines then gave place to white birches, (Betula alba, L.,) and 

 afterwards to alders, (Alnus glutinosa, L.,)and to hazel bushes, (Cory- 

 lus avellana, L.) 



This last stratum of the Sphagnum attains from three to ten feet 

 thickness, according to circumstances. It concludes the formation of 

 the Skovmose, the surface of which finally becomes more or less solid 

 and firm. 



As a matter of course, the complete development of all the strata 

 spoken of can be observed only in the central region of the swamps, 

 where the depth is sufficient. Towards the edges of the swanips, 

 the formation is more compressed and restricted within narrower 

 limits of thickness. 



We do not yet possess any data respecting the time which has been 

 required for these peat-bogs to reach their last stage of growth. Mr. 

 Steenstrup estimates that in order to form one of these masses of peat 

 ten or twenty feet thick it has required at least four thousand years, 

 but he thinks that this may be only the third or the quarter of the 

 necessary time. 



It is often supposed that the formation of the peat is more or less 

 rapid, because pits whence it has been extracted become filled up again 

 in a more or less short period. Mr. Steenstrup sees in this phenome- 

 non the effect, less of the growth of the turf, which is extremely slow, 

 than of a filling up from below, by the hydrostatic pressure of the sur- 

 rounding swamp. And, accordingly, the peat-bogs become altogether 

 exhausted in the long run, as Denmark has actually experienced. 



Exterior Forest Zone of the Skovmose. — Above the clayey de- 

 posit spoken of, which constitutes the basis of the basin containing the 

 swamp, there appear, firstly, the recumbent trunks of the pine (Pinus 

 silvestris) in great numbers. They attain a diameter of three feet, 

 with a corresponding length, and their magnificent stature proves on 

 one hand that they found conditions of existence favorable to their 

 growth, and on the other that they grew very closely together, form- 

 ing forests of pure species, unmixed with any others ; for when pine 

 trees are not thus closely arranged they do not arrive at this straight 

 and tall stature. The species certainly was the same as our present 

 one, only the cones were on the average a little smaller, and the bark 

 was thicker than at the present. 



The presence of the pine in the peat-bogs of Denmark was the more 

 surprising, that in our day the species has entirely disappeared from 

 the country, the pines that are found there now having been introduced 

 in modern times. This is so true, that no historical or even traditional 

 data makes the slightest allusion to the pine, as having grown natur- 

 ally in Denmark ; therefore, the species must have disappeared a 

 very long time ago. As for the firs (Pinus abies) it never occurred 

 spontaneously in Denmark, not even in ancient times. They have 

 begun to plant it since the end of the last century. 



