GENERAL FEATUEES, ETC. 



451 



times, and its underground galleries now spread over an area of 89 square miles. 

 In time of war they have frequently afforded a safe retreat to the inhabitants of 

 the country, aud are remarkable, moreover, on account of the large number of 

 fossils they have yielded. 



The country to the north of these hills is of tertiary or post-tertiary formation, 

 but it is by no means a dead level, for swellings of the ground and even hills 

 occasionally rise above the bottom-lands, and diversifj^ its surface. The Veluice, 

 a tract to the north of the Rhine, is thus favoured. Its hills, being for the most 

 part clothed with heather, are a favourite ground with Dutch bee-masters. The 

 dunes in the same district have been planted with pines, and no longer threaten the 



Fig. 247. — The Quarries or the St. Pietersbeug. 

 Scale 1 : 25,000. 



2° 48 



2''49' 



The St. Pietersbeig is shown with its summit removed, so as to reveal the labyrinth of galleries. 

 1 Mile. 



cultivated fields, formerly placed under the protection of a zanclgraaf, or " sand 

 sheriff." Isolated hillocks occasionally rise above the dead flats occupied by 

 swamps and polders, the most notable among them being that surmounted by 

 the town of Bergen-op-Zoom. 



The waste of distant mountains has largely contributed towards the formation 

 of the hills. The Meuse brought down the débris of the Ardennes, the Rhine 

 gravel from the volcanic Seven Mountains, and even Scandinavia contributed her 

 share in erratic blocks and glacial drift. The erratic blocks have nearly all been 

 removed by quarrymen and lime-burners, but an abundance of pebbles and 

 gravel broadly distinguishes these eastern heights from the dunes on the coast. 



Vast in extent are the peat bogs, occupying as they do nearly the whole of 



