Ch. XI.] STEATA CONTAINING EECENT SHELLS. 129 



have been earned southward cannot be doubted ; those of granite, for 

 example, scattered over large districts of Russia and Poland, agree pre- 

 cisely in character 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 mineral characters 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 super- 

 position at several points to strata containing recent shells. Thus, for 

 example, in European Russia, MM. Murchison and De Verneuil 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 inhabiting the arctic sea, on which rested the boulder forma- 

 tion, containing large erratics. 



In Sweden, in the immediate neighborhood of Upsala, I had observed, in 

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

 layer of marl, evidently formed originally at the bottom of the Baltic, by 

 the slow growth of the mussel, cockle, and other marine shells of living spe- 

 cies, intermixed with some proper to freshwater. 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 fee,t 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 continued 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 Denmark, also, recent shells 

 have been found in stratified beds, closely associated with the boulder 

 clay. 



It was stated that in Russia the erratics diminished generally in size 

 in proportion as they are traced farther from their source. The same 

 observation holds true in regard to the average bulk of the Scandinavian 

 boulders, when we pursue them southwards, from the south of Norway 

 and Sweden through Denmark and "Westphalia. This phenomenon is 

 in perfect harmony with the theory of ice-islands floating in a sea of 



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

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