690 MR DAVID MILNE HOME ON THE BOULDER-CLAY OF EUROPE. 



two sets of glacial striae are seen crossing each other. "The strong normal 

 streaks athwart the hill from the N.W., a direction in which no local or limited 

 mass of ice could move, are chequered with fainter streaks, produced by this 

 simple down hill movement, which happens to be from W.S.W." 



12. The changes in the relative levels of sea and land, and the other events 

 referred to in this paper, may be briefly summarised thus — 



(1.) A period existed subsequent to the epoch of the lowest Norfolk boulder- 

 clay before referred to, when the area now forming the British Isles was con- 

 nected with Continental Europe on the one hand, and with North-Eastern Europe 

 on the other, so as to permit terrestrial animals and flora to migrate from both 

 continents. 



At this period the climate was colder than at present, yet not so severe as to 

 prevent the growth of Scotch fir, spruce, yew, oak, and beech, the remains of 

 these trees having in England been found under the upper boulder-clay.* 



(2.) Afterwards a great part of North- Western Europe was submerged, so 

 that in Scotland, and a considerable part of England and Ireland, mountains less 

 than 2500 feet above the present sea-level disappeared. 



Most of the land animals which had inhabited the country (including elephants, 

 rhinoceros, rein-deer, musk, ox, &c.) would perish by starvation and drowning. 



The climate became colder, so as to be suited for mollusks and other marine 

 animals of an Arctic type. 



Shore-ice was formed along the coasts, and icebergs would be drifted by a 

 current from the north-west over North- Western Europe in great numbers, 

 stranding and grating along the sea-bottom. 



It was at this time, probably, that boulders were transported and lodged on 

 the slopes of hills at great distances from the parent rocks ; that rock surfaces, 

 especially on the ridge and crests of hills, were smoothed, and that the beds of 

 mud, gravel, and sand covering the rocks below the sea, were ploughed into and 

 frequently changed into the tenacious, unstratified deposit called boulder-clay. 



The Arctic current which brought these icebergs, if it flowed from Behring's 

 Straits eastwards across Hudson's Bay, might have aided in the transport of 

 North Pacific mollusks and Labrador plants to Great Britain. 



(3.) The next change was the elevation of Britain and the adjoining con- 

 tinental districts to such a height, that what is now sea between Great Britain 

 and the Continent and Ireland, became dry land, allowing again a migration of 

 plants and animals. 



The land probably rose high enough to admit the formation of glaciers in the 

 principal valleys, in which case much of the boulder-clay previously formed when 



* Sir Ch. Lyell gives proof that the forest and lignite beds of Cromer were preceded and 

 followed by a period of glacial cold. These forest and lignite beds " underlie the great mass of 

 glacial drift, in part unstratified, and containing boulders and angular blocks transported from great 

 distances." — Princ. vol. i. p. 197. 



