NOTES ON THE GEOLOGY OF THE TROAD. 627 



36. Notes on the Geology of the Troad. A brief Summary of the 

 Results derived from the Observations made in connexion with 

 the Assos ( U.S.) Expedition. By J. S. Diller, Esq., Geologist 

 to the Expedition. Communicated, with Notes, by W. Topley, 

 Esq., F.G.S. (Read June 6, 1383.) 



The terranes of the Troadic peninsula comprise a variety of stratified 

 and massive or eruptive rocks. The former, excepting the most 

 recent deposits, which are not considered in this connexion, may- 

 be divided into three groups according to their mineralogical 

 conditions and geological age. 



The most ancient group is highly crystalline and, in all probability, 

 belongs to the so-called mica-schist zone of the " Grundgebirge " or 

 Archeean formation. 



The youngest group, embracing the Miocene and Pliocene Tertiary 

 deposits, is, at least in part, well characterized by its fossils. 



The middle group is defined by the widely separated limits of the 

 other two groups. It embraces rocks which may be Palaeozoic or 

 Prepalaeozoic, as well as others wnich are probably of Cretaceous and 

 Eocene age. 



Crystalline Schists. — The crystalline schists have their greatest 

 development in Mount Ida, of which they form almost the entire 

 mass. They are of many varieties, all conformably interstratified, 

 as if belonging to the same great terrane. 



True gneisses are not abundant, and occur chiefly upon the north 

 side of Mount Ida, under such conditions that they appear to overlie 

 the schistose rocks. In Hadji-eulduren-dagh the mica is in large 

 part replaced by hornblende, so that the gneiss has a dioritic aspect. 



In the schistose rocks (chiefly amphibolites) hornblende is one of 

 the most widely distributed and abundant minerals. It generally 

 appears as actinolite, and not unfrequently constitutes almost the 

 whole of the rock in which it occurs. With amphibole are associated, 

 besides felspar, at times more or less quartz, epidote, magnetite, 

 titanite, and rutile. True mica-schists are of less common occurrence, 

 interstratified with the amphibolites. 



Near the centre of Mount Ida the oldest rocks crop out, and among 

 them is talc-schist, which, by the gradual addition of olivine, passes 

 into small lenticular masses composed almost exclusively of the latter 

 mineral. According to the nomenclature of Brogger this rock should 

 be called olivine-schist. By alteration it gives rise to serpentine, 

 with the characteristic reticulated structure which ever marks the 

 serpentine derived from olivine. Occasionally the fibrous serpentine 

 forms veins of considerable size in the adjacent rocks. 



The olivine-schist, where purest, has no schistose structure. The 

 passage from talc-schist, in which no olivine occurs, to that composed 

 almost entirely of olivine, takes place sometimes within a short 

 distance. The chief mass of the rock, however, is a middle stage 



