Mat 1902.] BOTANICAL SOCIETY OF EDINBUEGH. 243 



glacial conditions, and which are remarkably well seen in 

 the cliffs on either side of Cromer. With these it is not 

 necessary to deal in any detail, because we are only con- 

 cerned here with the fact that a long and complex series 

 of events followed the close of the period when the Forest 

 Bed was formed, all of which were connected with the 

 fact that an Age of Snow had set in, that it continued here 

 a very long time, and that the area over which the nivosal 

 conditions obtained became larger and larger as time 

 went on. 



The essential features of this history which most con- 

 cern us are, I think, — (1) the long duration of this Age 

 of Snow ; (2) the fact that it came on very gradually : (3) 

 that the conditions to which it was due emanated, in the 

 first instance, from Scandinavia; (4) that the "Gulf Stream" 

 was in full operation all the time off the west of Britain 

 and close to Xorway : and (5) that the land stood much 

 higher above the sea than it does at present. Many facts 

 incline me to the belief that it was the elevation of the 

 land which gave rise to these nivosal conditions, and it 

 was also that same factor which helped to bring the river- 

 valleys and the coast-line of the British Isles into some- 

 thing like their present form. 



The sequence of events, so far as the plants are con- 

 cerned, was, it seems to me, somewhat as follows : — First, 

 the condensation of the aqueous vapour (derived from the 

 aerial component of the "Gulf Stream") in the form of snow 

 instead of rain, first of all on the mountain summits, and 

 then, as time went on, lower down, and on the lowlands, 

 farther out from the mountain massifs. Mountain plants, 

 if they were to hold their own, then had to extend their 

 range outward in the direction of the lowlands. The lowland 

 plants also had uncongenial climatal conditions against them 

 on one side, and they had also the alpine invaders entering 

 into competition with them. So, except on the southern 

 and south-eastern margins of their normal stations, they 

 too were not able to hold their own. Thus, as time went 

 on, they gradually extended their range in the direction 

 away from the margin of the snow, and in the opposite 

 direction they slowly yielded place to the Alpine flora, 

 which was, in turn, also changing ground in the same 



