178 PREHISTORIC EUROPE. 



of Scotland are now known to have contained glaciers. It is fur- 

 ther known that those glaciers attained so great a thickness that 

 in many cases their upper strata overflowed the limits of the 

 valleys, and became confluent across the summits of the inter- 

 vening high grounds, which are striated in precisely the same man- 

 ner as the lower slopes. These unmistakable glacial markings 

 have been traced up to a height of more than 3000 feet, and the 

 general evidence shows that during the climax of the Ice Age 

 only the highest hill-tops projected above the level of the great 

 sheet of ice which overwhelmed all the mountainous regions of 

 the country. More than this, glacial strise, furrows, and roches 

 moutonnees have been traced throughout all the lowland districts, 

 and the trend of these indicates, in a manner not to be mistaken, 

 that the districts referred to have been ploughed over by glacier- 

 ice coming from the more elevated tracts of the country. And 

 the thickness of that ice may be inferred from the fact that 

 isolated hills and hill-ranges, such as the Sidlaws, the Ochils, 

 the Lomonds, the Pentlands, the Campsies, and the rolling trap- 

 pean uplands of Lanarkshire and Ayrshire, are glaciated up to 

 and across their highest summits. All Scotland, in short, was 

 enveloped in ice, which levelled up the valleys, so that its higher 

 strata were enabled to grind across the tops of hills that rise to 

 within heights of 2000 and 3000 feet above the present sea-level. 

 Now it is evident that a mass of ice so thick as that could not 

 float off in shallow seas like those which immediately surround 

 us. We might have expected, therefore, to find that the islands 

 lying off our coast should afford some trace of glacial invasion. 

 And such is actually the case. The island of Bute, for example, 

 has been overflowed from end to end by ice streaming out from 

 the mountain-land of Argyleshire. Colonsay, in like manner, 

 disappeared underneath the glacier-ice that choked up the Firth 

 of Lome — in a word, not one of the Western Islands escaped. 

 Even the Outer Hebrides were swept across by the massive 

 mer de glace that pressed outwards to the ocean. 



The markings upon the rocks show us that, although all the 

 hilly district of Central Scotland, and every island, were thus 



