414 Br Boiics Researches in Geography, Natural 



occasionally contain near the Bosphorus, would lead us to 

 place tkern in the Silurian system. 



Secondary rocks. — The only rocks belonging to the secon- 

 dary class seem to be cretaceous, which may be divided into 

 three groups, namely, 1*/, siliceous beds with little limestone ; 

 2d, calcareous beds often containing hippurites ; and 3d, a for- 

 mation very rich in nummulites. 



The siliceous deposit constitutes the centre of Servia and 

 certain portions of Eastern Mcesia. The hippurite limestone 

 forms a large portion of the Balkan, of Mount Pindus, and of 

 Transylvania, and a still larger part of Bosnia and Croatia. 

 The nummulite formation is seen in Epirus, and in much of 

 the western portion of Turkey. The inferior or siliceous 

 beds of the cretaceous formation contain vegetable remains 

 (Fucoides), together with various shells characteristic of chalk, 

 such as echini, orbitolites, ostrece, plageostoma, &c. The supe- 

 rior beds consist of green sand in their lower, and of calca- 

 reous beds with flints in their upper portions. The petrifac- 

 tions are like those of the chalk of the west of Europe. They 

 abound in caverns, in which the rivers frequently lose them- 

 selves, as happens also in Greece, where they are called Kato- 

 vothrons. 



This formation also comprehends, in Turkey, as in the Alps, 

 enormous masses of dolomite, and of limestone, full of cracks 

 and fissures, and containing a little magnesia. These dolo- 

 mites constitute a series of peaks in Albania and in other pro- 

 vinces. They appear to contain masses, though in appearance 

 small, of diorite. 



The nummulite formation contains much mineral pitch, 

 which, by being inflamed, appears to be the cause of the 

 Nymphosum of Plutarch, which exists in Dalmatia. Above 

 the chalk are extensive fresh-water formations, together with 

 enormous deposits of travertin. Large beds of conglomerate 

 are seen as a part of this formation in Thessaly. The partial 

 destruction of these beds has caused large blocks to be scat- 

 tered over the surface of the country, which appear like erra- 

 tic boulders, but which Dr Boue distinguishes from them. 

 There is every appearance that Thessaly was once a lake, 

 which drained off when the fissure at Tempe was produced. 



