126 BOULDER FORMATION. [Ch. XL 



CHAPTER XI. 



NEWER PLIOCENE PERIOD BOULDER FORMATION. 



Drift of Scandinavia, northern Germany, and Russia — Its northern origin — Not 

 all of the same age — Fundamental rocks polished, grooved, and scratched — 

 Action of glaciers and icebergs — Fossil shells of glacial period — Drift of eastern 

 Norfolk — Associated freshwater deposit — Bent and folded strata lying on un- 

 disturbed beds — Shells on Moel Tryfane — Ancient glaciers of North "Wales — 

 Irish drift. 



Among the different kinds of alluvium described in the seventh chapter, 

 mention was made of the boulder formation in the north of Europe, the 

 peculiar characters of which may now be considered, as it belongs in 

 part to the post-pliocene, and partly to the newer pliocene, period. I 

 shall first allude briefly to that portion of it which extends from Finland 

 and the Scandinavian mountains to the north of Russia, and the low 

 countries bordering the Baltic, and which has been traced southwards as 

 far as the eastern coast of England. This formation consists of mud, 

 sand, and clay, sometimes stratified, but often wholly devoid of stratifica- 

 tion, for a depth of more than a hundred feet. To this unstratified form 

 of the deposit, the name of till has been applied in Scotland. It gen- 

 erally contains numerous fragments of rocks, some angular and others 

 rounded, which have been derived from formations of all ages, both fos- 

 siliferous, volcanic, and hypogene, and which have often been brought 

 from great distances. Some of the travelled blocks are of enormous 

 size, several feet or yards in diameter ; their average dimensions increas- 

 ing as we advance northwards. The till is almost everywhere devoid of 

 organic remains, unless where these have been washed into it from older 

 formations ; so that it is chiefly from relative position that we must hope 

 to derive a knowledge of its age. 



Although a large proportion of the boulder deposit, or " northern drift," 

 as it has sometimes been called, is made up of fragments brought from a 

 distance, and which have sometimes travelled many hundred miles, the 

 bulk of the mass in each locality consists of the ruins of subjacent or 

 neighboring rocks ; so that it is red in a region of red sandstone, white in 

 a chalk country, and gray or black in a district of coal and coal-shale. 



The fundamental rock on which the boulder formation reposes, if it 

 consists of granite, gneiss, marble, or other hard stone capable of perma- 

 nently retaining any superficial markings which may have been imprinted 

 upon it, is usually smoothed or polished, and exhibits parallel striae and 

 furrows having a determinate direction. This direction, both in Europe 

 and North America, is evidently connected with the course taken by the 

 erratic blocks in the same district being from north to south, or if it be 

 20 or 30 degrees to the east or west of north, always corresponding to the 

 direction in which the large angular and rounded stones have travelled. 



