VOL. XVIII. (2) GLACIAL BOULDERS, BOURNVILLE 165 



that the boulders had been brought on floating icebergs when 

 Britain and all Northern Europe was sunk for a time under a 

 kind of shallow Arctic Ocean. 



At the present day the general working theory of the 

 majority of geologists is that many boulders were brought 

 into the Midlands from distant mountainous regions by means 

 of a great ice-sheet, like the present ice-sheets of Greenland and 

 the Antarctic Continent, which great ice-sheet moved mainly 

 from north to south, and buried up in a continuous white 

 mantle the British Islands and the neighbouring seas, moving 

 almost as far south as the valley of the Thames. 



Our present knowledge of the wide spread extent of the 

 Midland glacial deposits, boulder clays, gravels, brick clays 

 and the erratic blocks has been of slow growth. It has been 

 accumulated stage by stage, and from time to time by a large 

 number of Midland workers. Many of the earliest and most 

 enthusiastic of them, Mr Mackintosh, Dr Crosskey, and 

 Mr Jerome Harrison are, alas, no longer with us. Mr C. J. 

 Woodward, Mr Fred Martin, Mr Mantle, Dr Matley, and others 

 still remain to us, while fresh workers are quietly advancing 

 our knowledge. 



Of geologists working elsewhere, we owe, of course, a 

 debt of gratitude to Professor James Geikie, his brother 

 Sir Archibald Geikie, Professor Bonney, the late Professor 

 Carvill Lewis, Professor Percy Kendall, Dr Marr, Professor 

 Penck, and other authorities on Glaciology in general. 



THE GREAT ICE-SHEET 



The present trend of collective opinion is to regard it as 

 a well established theory that the great Ice Age was a time of 

 more or less gradually increasing cold, the effects of which 

 led to a greater and greater accumulation of snow and ice. 

 This began in the northern regions and on the higher grounds, 

 and gave origin in the first instance to snowfields and glaciers, 

 which by their growth and coalescence eventually developed 

 into the great Ice-Sheet itself. With the gradual ameliora- 

 tion of the climate towards the close of the Ice Age, the ice 



