On. XII] OF KORTHEEN ORIGIK 139 



considerably colder tlian now during the period under consideration, 

 owing probably to the greater area and height of arctic lands, and to the 

 quantity of icebergs which such a geographical state of things would 

 generate, it may be well to reflect before we proceed farther on the en- 

 tire modification which extreme cold would produce in the operation of 

 those causes spoken of in the sixth chapter as most active in the forma- 

 tion of alluvium. A large part of the materials derived from the detritus 

 of rocks, which in warm climates would go to form deltas, or would be 

 regularly stratified by marine currents, would, under arctic influences, 

 assume a superficial and alluvial character. Instead of mud being carried 

 farther from a coast than sand, and sand farther out than pebbles, — instead 

 of dense stratified masses being heaped up in limited areas, along the borders 

 of continents, — nearly the whole materials, whether coarse or fine, would be 

 conveyed by ice to equal distances, and huge fragments, which water alone 

 could never move, would be borne for hundreds of miles without having 

 their edges worn or fractured ; and the earthy and stony masses, when 

 melted out of the frozen rafts, would be. scattered at random over the sub- 

 marine bottom, whether on mountain tops or in low plains, with scarcely 

 any relation to the inequalities of the ground, settling on the crests or 

 ridges of hills in tranquil water as readily as in valleys and ravines. 

 Occasionally, in those deep and uninhabited parts of the ocean, never 

 reached by any but the finest sediment in a normal state of things, the 

 bottom would become densely overspread by gravel, mud, and boulders. 



In the Western Hemisphere, both in Canada and as far south as the 

 40th and even 38th parallel of latitude in the United States, we meet 

 with a repetition of all the peculiarities which distinguish the European 

 boulder formation. Fragments of rock have travelled for great distances 

 from north to south ; the surface of the subjacent rock is smoothed, 

 striated, and fluted ; unstratified mud or till containing boulders is asso- 

 ciated with strata of loam, sand, and clay, usually devoid of fossils. 

 Where shells are present, they are of species still living in northern seas, 

 and half of them identical with those already enumerated as belonging 

 to European drift 10 degrees of latitude farther north. The fauna also of 

 the glacial epoch in North America is less rich in species than that now 

 inhabiting the adjacent sea, whether in the Gulf of St. Lawrence, or off 

 the shores of Maine, or in the Bay of Massachusetts. At the southern 

 extremity of its course, moreover, it presents an analogy with the drift of 

 the south of Ireland, by blending with a more southern fauna, as for 

 example at Brooklyn near New York, in lat. 41° N., where, according 

 to MM. Redfield and Desor, Venus mercenaria and other southern species 

 of shells begin to occur as fossils in the drift. 



The extension on the American continent of the range of erratics 

 during the Pleistocene period to lower latitudes than they reached in 

 Europe, agrees well with the present southward deflection of the isother- 

 mal lines, or rather the lines of equal winter temperature. It seems that 

 formerly, as now, a more extreme climate and a more abundant supply of 

 floating ice prevailed on the western side of the Atlantic. 



