716 



REPOllT — 1892. 



of the Scotch fir, in which also, besides a number of sub-alpine plants, more 

 southern plants, as Betula verrucosa, occurred. At last the climate again became 

 dry, and the formation of tufa ceased anew. After that time Picea Abies, Acer 

 platanoides, and other plants of a more southern type immigrated into the valley.* 



In the case of these tufas there is no doubt that the alternation of tufa beds 

 and clays is due to a climatic period of long duration (probably caused by the 

 precession of the equinoxes). In a paper, On Variations of Climate in the Course 

 of Time (' Nature,' 1886), I have given many reasons for the occurrence of such 

 a period. And in a later paper, On the Probable Cause of the Displacement of 

 Shore-lines (London, Edinburgh, and Dublin, ' Phil. Mag.,' 1889, pp. 405, 487, 

 reprinted in the 'Smithsonian Eeport,' Washington, 1890, p. 326), I have tried to 

 show how, with the aid of alternating strata, we may possibly get to a computation 

 of geological time. It is no objection to this theory that alternating strata may 

 be formed also by other and more local causes. We should try to learn to dis- 

 tinguish between such local alternations and those which are caused by more 

 generally operating and probably cosmical causes. 



Lastly, I would remark that in Denmark and Southern Norway the alternating 

 layers of forest and peat in peat bogs show more alternations than the tufas and 

 peat of our mountain valleys, the reason being probably that glaciers Ungered in 

 the mountain valleys a long time after the lowlands had been free of ice and snow. 



7. Fossil Arctic Plants found near Edinburgh. 

 By Clement Reid, F.L.8., F.G.S. 



Recent discoveries by Mr. Bennie, of the Geological Survey, have brought to 

 light a series of silted-up tarns or small lochs in the neighbourhood of Edinburgh. 

 These tarns seem to have lain in irregular hollows left on the retreat of the ice, 

 for the lowest deposits usually yield remains of arctic plants. The principal 

 localities for these plants are Corstorphine and Hailes. Trees, except perhaps the 

 alder, are entirely missing in the lower deposits, and the vegetation consists mainly 

 of dwarf willow and birch, with a few herbaceous plants, of species still living 

 within the Arctic Circle. The list now includes the following plants, those 

 marlced with an asterisk being arctic species no longer living in the lowlands of 

 Scotland : — 



Flowering Plants. 



Ranunculus aquatilis, Linn. 



„ repens, Linn. 



Viola (?). 



Stellaria media, Cyr. 

 Rubus sp. 



*Drj'as octopetala, Linn. 

 Poteutilla sp. 

 Poterium sp. 

 Hippuris vulgaris, Linn. 

 Myriophyllum spicatum, Linn. 

 Taraxacum officinale, Web. 

 Andromeda polyfolia, Linn. 

 Menyanthes trifoliata, Linn. 



*Oxyria digyna. Hill, 

 *Betula nana, Linn. 



Alnus (?). 



Salix repens, Linn. 



* „ herbacea, Linn. 



* „ polaris, AV^ahlb. 



* ,, reticulata, Linn. 

 Empetrum nigrum, Linn. 

 Potamogeton sp. 

 Eleocharis palustris, R. Br. 

 Scirpus pauciflorus, Lightf. 



„ lacustris, Linn. 

 Carex, 2 sp. 



Mosses (determined iy Antony Gepp, F.L.S.) 

 Barbula fallax, Hedwig. Philonotis fontana, Brid. 



fragilis, Bruch & Sch. 

 Grimmia sp. 

 Racomitrium sp. 



Aulacomnion palustre, Schw, 

 Webera sp. 

 Bryum sp. 



' A fuller description of these tufas is given in Engler's Botanische Jahrhilclier 

 for this year. 



