76 



The first point to make clear is that the climatic changes we 

 speak of were very sweeping, covering a wide area in Europe, 

 and perhaps affecting the whole northern hemisphere. They were 

 not slight changes caused by varying elevations of the land, or 

 anything of that sort. 



It is obvious that the temperature of the sea can have little to 

 do with variations in the height of the land. Our warmth in the 

 south and west of England now comes from the Atlantic — how 

 was the Atlantic then affected ? 



A few years ago we could not have answered this question 

 with any degree of confidence; but whilst I was in charge of the 

 Geological Survey of the south of England I was asked by 

 one of my colleagues to come over to the Isles of Scilly and see 

 some curious boulder-beds. The Isles of Scilly are composed of 

 granite, and of nothing but granite; the boulders there found, 

 however, included a variety of rocks — sedimentary, igneous, and 

 metamorphic. The most abundant were of a pale-reddish sand- 

 stone, unlike anything in Cornwall or Devon. These were 

 subsequently identified as coming from the Upper Old Red 

 Sandstone of the south of Ireland. A large proportion of these 

 blocks had been scratched, striated, or polished by moving ice — 

 nothing else gives these curious facetted surfaces covered with 

 parallel scratches. The erratic blocks usually occurred only a few 

 feet above the sea-level, though in certain places they could be 

 traced up gentle slopes nearly to the highest points on the Isles. 

 These places were in bays open to the west wind — just the sort of 

 places where the ice floes would accumulate, and, driven by the 

 spring gales, would be forced up the slope and piled high above the 

 sea-level. In places where abrupt cliffs face the sea the boulders 

 were only found near their foot. 



This compels us to picture a time when the Isles of Scilly, 

 now surrounded by a sea so warm that frost scarcely ever touches 

 the vegetation, lay in an ocean so cold that ice-floes could travel 

 all the way from the south of Ireland, bearing with them numerous 

 ice-scratched blocks of sandstone. Possibly with this floe-ice were 

 a certain number of bergs broken off from the Irish glaciers, which 

 certainly descended to the sea-level and sent tongues out into the 

 Atlantic. Most of the erratics, however, look like beach-stones 

 frozen into the ice-foot, and drifted away when the ice broke up in 

 spring. 



It may be said that this Arctic sea, though it affected the 

 Isles of Scilly, did not reach as far east as Bournemouth and the 

 Isle of Wight. However, the evidence is equally strong in the 

 Selsey Peninsula, where a very similar erratic-bed if found. The 

 Selsey erratics are most instructive. Few of them are striated, 

 and the striation is probably only such as would be caused by ice 

 driven by the tide across submerged reefs. A striated block I 

 found is composed of hard fossiliferous sandstone, and comes 

 probably from Bognor Ledge, a reef of rocks running a good way 

 out to sea at Bognor. 



