364 



TEANSPOETATION OF SOLID MATTEK 



[Ch. XVI. 



buoyant, and easily borne along by a feeble current. The 



ice, mor 

 streams 



melts very slowly at the bottom 



om 



sequel of ground-ice. 



As we travel eastward in Europe in the latitudes of Great 



more 



regularly frozen over. M. Lariviere relates that, being at 

 Memel on the Baltic in 1821, when the ice of the river 

 Niemen broke up, he saw a mass of ice thirty feet long: which 



stream 



In 



the middle of it was a triangular piece of granite, about a 

 yard in diameter, resembling in composition the red granite 

 of Finland.* 



When rivers in the northern hemisphere flow from south 

 to north, the ice first breaks up in the higher part of their 

 course, and the flooded waters, bearing along large icy frag- 

 ments, often arrive at parts of the st: 



earn 



firmly frozen over. Great inundations are thus frequently 

 occasioned by the obstructions thrown in the way of the 



b 



Mackenzie 



America, i 

 of Siberia. 



map 



fig. 3, p. 182.) A partial stoppage of 

 this kind occurred in Jan. 31. 1840 in the Vistula, about a 

 mile and a half above the city of Dantzic, where the river, 

 choked up by packed ice, was made to take a new course over 

 its right bank, so that it hollowed out in a few days a deep 



many 



from 40 to 60 feet hig 



In Canada, where the winter's cold is intense, in a latitude 

 corresponding to that of central France, several tributaries 



of the 



Lawrence 



while they remain frozen over lower down, and thus large 



unbroken 



of ice below. Then begins what is called the packing of the 

 drifted fragments ; that is to say, one slab is made to slide 

 over another, until a vast pile is built up, and the whole 

 being frozen together, is urged onwards by the force of the 



* Consid. sur les Blocs Errat. 1829. 



