SWAN PRINCES ISLANDS. 63 



The remaining island (Oxia) I did not visit. 



10. General observations. — Throughout the whole examination of 

 the Princes Islands I have been greatly struck with the regularity 

 of the line of dip whenever local causes do not occur to affect it ; 

 it may be taken to vary from S. 45° W. to S. 75° W. ; and this 

 regularity is very marked in the quartz beds throughout, which 

 have greatly served as a guide in arriving at this conclusion. I have 

 also examined the coast of the mainland to the north-east of Prin- 

 kipo, and find the dip there, at the village of Khartal and eastward, 

 from S. Qq"" W. at 35°, to S. 35° W. at 75° to 80°, for a distance 

 of about a quarter of a mile ; and then it suddenly reverses and 

 dips north-east, and continues so as far as I went, or about two miles 

 and a half along the beach towards the village of Pendik. The 

 description of these beds will be reserved for a future memoir. 



If we assume that the line of dip is about S. 45° W., then we must 

 conclude that the "Red Sandstones" of Proti come in between the 

 Island of Prinkipo and the mainland. But on the other hand, if we 

 assume the full dip to be about S. 75° W., then the " Red Sand- 

 stones " would come in between Plati and Prinkipo, on the line of 

 Antigoni, and would correspond with the white and purple sand- 

 stones of the latter island ; and I am inclined to take this latter as 

 the correct view of the case. 



And if we measure a line from Plati or Oxia to the mainland, in 

 the full rise of the strata we have a distance of about five to six 

 miles, represented in all probability by a perpendicular thickness of 

 about 18,000 to 20,000 feet of strata, which have been almost entirely 

 swept away from the Devonian mainland in ages past, and are at 

 present represented by the Princes Islands. 



And here, in conclusion, it will not be out of place to remark that 

 in the course of my many observations on the geology of the Bithy- 

 nian peninsula, from many points, I have found the strata to be dis- 

 posed in a basin-like form, the line of the Bosphorus forming the 

 western lip of the basin, and the full rise of the strata gradually 

 sweeping round to the north on the northern or Black-Sea side, and 

 to the south on the southern or Sea-of-Marmora side, the centre of 

 the basin aj)pearing to be the high chain of mountains of Kaish Dugh, 

 the Two Brothers, &c. ; but this I do not yet know for certain ; nor 

 have I yet visited the eastern side of the Devonian strata, and 

 therefore I cannot say if the basin-shape is preserved throughout. 

 The disposition of the strata of the Princes Islands clearly corresponds 

 with these observations. 



