GEOLOGY OF THE TBOAD. 631 



coloured, soft, light and porous, and generally shows no trace of 

 effervescence in hydrochloric acid. In general appearance it closely 

 resembles an impure siliceous limestone out of which the greater 

 portion of the carbonate of lime has been dissolved. Having a 

 thickness of about one hundred and thirty metres, it becomes the 

 chief topographical determinant of that region, and gives rise to 

 profound gorges and bold escarpments. Throughout the greater 

 portion of the mass it is uniformly fine-grained, but under the 

 microscope it has the structure of a tufa. 



The upper beds of the series, consisting of thin freshwater lime- 

 stones, sandstones, shales, and a large proportion of stratified tufas 

 with conglomerates, have not been seen east of Demiradji-kieui. 

 The fossils collected were found in this portion of the series and it 

 is evident that the ejection of the andesites began before the depo- 

 sition of those beds was completed. 



Numerous oscillations of the land, as indicated by the varying 

 character of the strata, must have occurred during the Miocene and 

 Pliocene periods ; and in all probability these movements were con- 

 nected with the extrusion of the eruptive rocks so abundant in the 



Massive Rocks.— The massive rocks of theTroad belong in part to 

 those of pre-Tertiary origin ; but the greater portion were ex- 

 truded since the beginning of the Tertiary Period. The older group 

 includes biotite-hornblende-granite, quartz-porphyry, quartz- diorite, 

 augite-porphyrite, melaphyre, and serpentine; while the younger 

 group embraces liparites, andesites, augite-andesites, basalts, and 

 nepheline-b as alt . 



Older Series. — The biotite-hornblende-granite occurs in a large 

 mass forming the serrated ridge of Chigri-dagh. It is distinctly 

 younger than the highly crystalline stratified rocks which it pene- 

 trates, and is especially interesting from the fact that where it is 

 altered tbe titanite is changed to anatase. The alteration of titanite 

 and ilmenite to anatase is doubtless a common and widely spread 

 occurrence ; but as the" crystals of anatase are very small they have 

 generally been overlooked. 



The quartz-porphyries are chiefly microgranites, and are younger 

 than the biotite-hornblende-granite through which they have been 

 extruded. The dykes in which they occur are comparatively small 

 and do not exercise much influence upon the topographical features 

 of the country. 



The quartz-diorites form a number of comparatively small masses 

 about the base of Mount Ida, and are evidently younger than the 

 quartzose argillite of the middle zone of stratified rocks, which, in 

 one case, has been metamorphosed into a cordierite- and andalusite- 

 hornfels. It is to be especially noted that these eruptive rocks do 

 not, as was formerly supposed, enter into the structure of Mount Ida. 



The augite-porphyrites (diabase-porphyrites) and melaphyres are, 

 so far as is yet known, limited to five outcrops, all lying in a line near 

 the southern coast of the Troad, and which, with the exception of that 



Q.J.G.S. No. 156. 2y 



