of the Thracian Bosphorus. 389 



from Kavak to Anadoli-fanar they have a regular inclination towards the north. 

 They rest upon, or alternate with, trachytic rocks, more or less compact, and 

 occasionally passing into phonolite and basalt. In some places, especially 

 near Anadoli-fanar, dikes of the latter substance intersect the conglomerate 

 beds. The basalt occasionally assumes a columnar form, which is seen in the 

 greatest perfection at Yoom-bornou. The prevailing colour of these rocks is 

 greenish, owing to the presence of copper, a circumstance which gave the name 

 of Cyaneae to the weather-beaten rocks of the Symplegades. 



Near Pilbornou the conglomerate contains bowlders of a brownish trachyte, 

 softer than the greenish trachytic paste which envelopes them ; hence they 

 decompose with the weather, and give a honey-combed appearance to the 

 rock. The contrary, however, is more often the case, when the imbedded 

 fragments, being harder than their matrix, project above the general surface 

 of the rocks. 



These igneous formations contain many veins of red and white cornelian, 

 and varieties of chalcedony. In one place near Pilbornou the veins are perpen- 

 dicular and straight, intersecting the conglomerate, and cutting indiscrimi- 

 nately through the tufaceous paste and the imbedded fragments. — See the 

 accompanying wood-cut. 



a, a, Angular trachytic fragments imbedded in a tufaceous paste. 



b, 6, Veins of chalcedony traversing both the fragments and the paste. 



The deposition of these conglomerates appears to have been effected with 

 the assistance, if not solely by, water. The fragments imbedded in them, 

 though commonly angular, are sometimes rounded, and are contained in finely 

 laminated strata of volcanic sand. An instance of this, on (he north side of 

 Anadoli-fanar, is represented in the following wood-cut. 



3 E 2 



