Erratic Blocks in Plains, 231 



to make us suppose that tliere really existed in the North a 

 covering of ice, whose southern limits in Europe, at a certain 

 epoch, reached about 50^ N. Lat. I allude to that belt of 

 blocks observed by Russian geologists (see the letter from M. 

 de Meyendorf to M. Elie de Beaumont*), which extends 

 across the centre of Russia, by N. Nowogorod towards Pinsk, 

 as far as the confines of Silesia. It seems to me much more 

 natural to regard this limit as an isopagetic line (une ligne 

 hopagttlqueX)^ than as the southern limit of a current coming 

 from the North, and charged with blocks ; and this so much 

 the more, because the phenomenon of the transport of the 

 Scandinavian blocks extends not only into Russia and Ger- 

 many, but reaches the eastern coasts of England. In attri- 

 buting this effect to the action of a current, it would thus be 

 also necessary to imagine a fan-shaped current ; whereas a so- 

 lid limit, during a certain time, of a covering of ice as extensive 

 as that of the South Pole, obviates all the difficulties presented 

 by such a phenomenon, such as the continuity and the regula- 

 rity of the outlines, the uniform furrows of the polished sur- 

 faces of the North, the passage across the Baltic and the North 

 Sea of the blocks which lie on the surface of Germany and 

 of England, &;c. In a second zone of blocks, more to the 

 north than the first, and observed likewise in Russia, to the 

 south of the White Sea, and of the lakes of Onega and Ladoga, 

 we have a direct proof of the successive and slow retreat of 

 this covering of ice, a second isopagetic line more remote than 

 the first. If this covering of ice really existed, it must at 

 last have retired beyond the northern limits of the British 

 Islands, after having enveloped them partially or entirely ; but 

 so long as the northern ice had not retired to its present limit, 

 the climate of Europe must have been colder than it now is, 

 and, even when the primitive ice had abandoned the plains, 

 groups of glaciers must have remained in all mountainous 



• Archiv fur Wissenschaftliche Kundo von Eussland ; von Erman, Ber- 

 lin, 1841. 



t \aoi Tuytfos, that is to say, of equal ice ; in some sense the isotherme of 

 tlie outline of the northern covering of ice ; but as the limits of this ancient 

 ice do not coincide with the isothermal lines, I have been obliged to pro- 

 pose a new name. 



