138 THE ORIGIN AND HISTORY OF 



alluvium and boulder clay on the east and west coasts, both of 

 Scotland and England. These, as well as the extensive supply 

 now obtained from the gravels of the Uruguay and other rivers of 

 Brazil, have all been washed out of trap-rocks of one kind or 

 another. 



The principal seat of the Agate industry in Europe is situated 

 in the valley of the Nahe, a tributary of the Rhine, which it joins 

 between the celebrated Mouse tower and Bingen. It is a fine 

 valley, bounded especially in its upper reaches by hills which rise 

 in ragged and grotesque crags, crowned with the relics of ancient 

 baronial castles. The river rises in the mountains which bound 

 the valley of the Moselle east of Treves and Saarbruck. The 

 Hunsdruck hills, ranging on the left bank of the Nahe, are com- 

 posed of Devonian Strata. The hills at the source of the river 

 are of volcanic origin, and have burst through the coal-field of 

 Saarbruck, and for some distance along the valley of the Nahe 

 are surrounded by permian rocks. 



The volcanic rocks of the Galgenberg hills consist of the kind 

 of rock, called by Brougniart, melaphyre. "The uppermost bed," 

 says Dr. Billing — to whom I am indebted for much information 

 on this part of the subject — " is a flinty conglomerate, composed 

 of water-worn gravel, of quartz, porphyritic or other trap stones, 

 worn into pebbles, and united by ferruginous earthy matter, and 

 much burnt by a stratum of trap-rock below it, which forced it out 

 of its level to an inclination of nearly 40 degrees." Underlying 

 this conglomerate is a dark brown amygdaloidal trap more or less 

 porphyritic, and passing into greenstone ; and again below this 

 lies another kind of trap rock, which constitutes the hill Galgen- 

 berg, near the town of Idar, which is the depository of chalcedony 

 and agates, which has rendered the district celebrated. Below 

 this is another stratum of trap, darker, denser, and more of the 

 nature of basalt in the lower bed than in the higher, which con- 

 tains the agates. 



Agates formerly abounded in the alluvium at the foot of the 

 Galgenberg, and were readily collected ; and from very early 

 times workshops were established at Oberstein and Idar to grind, 

 cut, and polish them, There is documentary evidence that they 

 existed as early as 1454, and the industry was then an old one. 



