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DISTRIBUTION OF LEUCITE BASALTS. 



nepheline, though in some cases the quantity of nepheline is less than 

 in others. In a few localities olivine is added, and sometimes Hum- 

 boldtilite. This rock is well seen at Pohlberg, near Annaberg. In 

 the eastern Mittelgebirge, leucite-basalt occasionally contains a little 

 felspar, probably sanidine, and abounds in trichites. Near Aussig 

 the felspar is much more developed, and at Rothweil, in the Kaiser- 

 stuhl in Baden, the quantity of leu cite is diminished, so that it is not 

 always seen in hand specimens. At Stoffelskuppe in the Thiiringer- 

 wald, the leucite-basalt is free from felspar, and at Westberg, near 

 Hofgeismar, it is rich in large crystals of nepheline. In the Eifel, 

 the basaltic lavas contain leucite in many places, especially near Wehr 

 on the Laacher See, Veitskopf, the Forstberg, Burresheim, near St. 

 Johann. Other localities are Uedersdorf, Wehrbusch near Daun, and 

 Birresborn and Gerolstein. 



The famous porous basalt of Niedermendig, worked for mill- 

 stones and paving-stone, contains leucite and nepheline, with augite, 

 hauyine, and olivine, with triclinic felspar in some specimens. Chemi- 

 cally, these rocks may be compared with Malvern schists and shales. 



Leucite Basalts of North America. In North America this rock 

 is found in the Leucite Hills of Wyoming. The American leucite 

 rocks are yellowish grey and finely porous, and contain brownish mica 

 in long stripes peculiar to the rock. Leucite crystals are microscopic, 

 but abundant beyond anything known in European rocks. The 

 crystals are too small to show the twin structure indicated by alter- 

 nating dark and polarising bands. The rock contains pale-green prisms 

 and needles, which are referable to augite. There is a small quantity 

 of magnetite, and a few comparatively thick crystals of apatite. The 

 colour of the European leucite rocks is darker, because the augite 



