REVIEWS —THE STORY OF A BOULDER. 499 



And such has been the origin of the deep clay, "which, with its included and 

 accompanying boulders, covers so large a part of our country. When this arctic 

 condition of things began, the land must have been slowly sinking beneath the sea, 

 and so, as years rolled past, higher and yet higher zones of land were brought 

 do"wn to the sea-level, where floating ice, coming from the north-west, stranded 

 upon the rocks, and scored them all over as it grated along. This period of sub- 

 mergence may have continued until even the highest peak of the Grampians dis- 

 appeared, and, after suffering from the grinding action of ice-freighted rocks, 

 eventually lay buried in mud far down beneath a wide expanse of sea, over which 

 there voyaged whole argosies of bergs. When the process of elevation began, 

 the action of waves and currents would tend greatly to modify the surface of the 

 glacial deposit of mud and boulders, as the ocean-bed slowly rose to the level of 

 the coast line. In some places the muddy envelope was removed, and the subja- 

 cent rock laid bare, all polished and grooved. In other localities, currents brought 

 in a continual supply of sand, or washed off the boulder mud and sand, and theu 

 re-deposited them in irregular beds; hence resulted those local deposits of strati- 

 fied sand and gravel so frequently to be seen resting over the boulder clay. At 

 length, Oy degrees, the land emerged from the sea, yet glaciers still capped its hills 

 and choked its valleys ; but eventually a warmer and more genial climate arose, 

 plants and animals, such as those at present amongst us, and some, such as the 

 wolf, no longer extant, were ere long introduced ; and eventually, as lord of the 

 whole, man took his place upon the scene.* 



It is pleasant to mark, when once the true solution of a difficulty is obtained, 

 how all the discordant elements fall one by one into order, and how every new 

 fact eliciteti tends to corroborate the conclusion. In some parts of the glacial 

 beds, there occur regular deposits of shells, which must have lived and died in 

 the places where we find them. From ten to fifteen per cent, of them belong to 

 species which are extinct ; that is to say, have not been detected living in any sea. 

 Some of them are still inhabitants of the waters around our coasts, but the large 

 majority occur in the northern seas. They are emphatically northern shells, and 

 get smaller in size and fewer in number as they proceed southward, till they dis- 

 appear altogether. In like manner, the palm, on the other hand, is characteristi- 

 cally a tropical plant. It attains its fullest development in intertropical countries, 

 getting stunted in its progress towards either pole, and ceasing to grow in the 

 open air beyond the thirty-eighth parallel of latitude in the southern hemisphere, 

 and the forty- fifth in the northern. So, too, the ivy, which in our country hangs 

 out its glossy festoons in every woodland, and around the crumbling walls of 

 abbey, and castle, and tower, is nursed in the drawing-rooms of St. Petersburgh 

 as a delicate and favourite exotic. In short, the laws which regulate the habitat 

 of a plant or an animal are about as constant as those which determine its form. 

 There are, indeed, exceptions to both. We may sometimes find a stray vulture 



* The reader who wishes to enter more fully into the geological effects of icebergs, should 

 consult the suggestive section on that subject in De la Beche's Geological Ohsener ; also 

 the Principles, and Visit to the United States, of Sir Charles Lyell, with the various au- 

 thorities referred to by these writers. 



