150 GLACIATION OF RUSSIA. [Ch. XII 



have also been conveyed, evidently by the aid of floating ice. The 

 southern and southeastern limits of this drift have been well marked 

 out by Sir Roderick I. Murchison and his fellow-laborers, M. de Yer- 

 neuil and Count Keyserling, in a map illustrating their great work on 

 the geology of Russia; and they have pointed out how this drift 

 " proceeded eccentrically from a common central region." 



It appears from their observations that the blocks, scattered over 

 large districts of Russia and Poland, agree precisely in mineral charac- 

 ter with rocks of the mountains of Lapland and Finland ; while the 

 masses of gneiss, syenite, porphyry, and trap, strewed over the low 

 sandy countries of Pomerania, Holstein, and Denmark, are identical 

 in their composition with the mountains of Norway and Sweden. 



It is found to be a general rule in Russia, that the smaller blocks 

 are carried to greater distances from their point of departure than the 

 larger; the distance being sometimes 800, and even 1000, miles from 

 the nearest rocks from which they were broken off; the direction 

 having been from N.W. to S.E., or from the Scandinavian mountains 

 over the seas and low lands to the southeast. That its accumulation 

 throughout this area took place in part during the Post-pliocene 

 period, is proved by its superposition at several points to strata con- 

 taming recent shells. Thus, for example, in European Russia, Sir R. 

 Murchison and his associates found, in 1840, that the flat country 

 between St. Petersburg and Archangel, for a distance of 600 miles, 

 consisted of horizontal strata, full of shells similar to those now in- 

 habiting the Arctic Sea, and on these rested the boulder formation, 

 containing large erratics. 



In Sweden, in the immediate neighborhood of Upsala, I had ob- 

 served, in 1834, a ridge of stratified sand and gravel, in the midst of 

 which occurs a layer of marl, evidently formed originally at the bot- 

 tom of the Baltic, by the slow growth of the mussel, cockle, and 

 other marine shells of living species, intermixed with some proper to 

 fresh water. The marine shells are all of dwarfish size, like those 

 now inhabiting the brackish waters of the Baltic ; and the marl, in 

 which myriads of them are imbedded, is now raised more than 100 

 feet above the level of the Gulf of Bothnia. Upon the top of this 

 ridge repose several huge erratics, consisting of gneiss for the most 

 part unrounded, from 9 to 16 feet in diameter, and which must have 

 been brought into their present position since the time when the 

 neighboring gulf was already characterized by its peculiar fauna.* 

 Here, therefore, we have proof that the transport of erratics con- 

 tinued to take place, not merely when the sea was inhabited by the 

 existing testacea, but when the north of Europe had already assumed 

 that remarkable feature of its physical geography, which separates 

 the Baltic from the North Sea, and causes the Gulf of Bothnia to 

 have only one-fourth of the saltness belonging to the ocean. In Den- 



* See paper by the Author, Phil. Trans., 1835, p. 15. 



