SWAN PRINCES ISLANDS. 53 



2. On the Geology of the Princes Islands, in the Sea of Marmora, 

 Turkey. By W. R. Swan, Esq. 



[Communicated by Sir R. I. Murchison, Bart., K.C.B., F.R.S., F.G.S., &c.] 



(Read June 19th, 1867 *.) 



Contents. 



5. Island of Petala or Beta. 



6. Island of Antigoni. 



7. Island of Proti. 



1. Introduction. 



2. Island of Prinkipo. 



a. Trachytic rocks. 



b. Trap rocks. 



c. Primary sedimentary strata. 



3. Island of Andirovitho. 



4. Island of Cbalki. 



8. Island of Niandros. 



9. Island of Plati. 



10. General Observations. 



1. Introduction. — It was during a visit to Prinkipo, the largest 

 of the Princes Islands, in the summer of 1864, that I first had an 

 opportunity of studying the geological features of that island ; and 

 the discoveries I then made were of so interesting a character as 

 to induce me to continue the examination of the remaining eight 

 islands. 



Before going into a detailed account of each island, I will here 

 relate some of the chief points of interest met with, namely : — 



(1.) The existence of a considerable tract of Devonian strata, 

 partly fossiliferous, in several of these islands, of an age different 

 from that of the beds of the Bosphorus, which latter I have already 

 shown, in a former paper to the Geological Society f, to belong to 

 the lowest of the Devonian series of the Bhine. Also the existence 

 of the remains of " fish" in the above strata, and an ancient " coral 

 reef." 



(2.) That the rocks which form the remaining portions of these 

 islands are trachytic, and of younger age than the Devonian strata. 



(3.) That the trap rocks of these islands are of younger age than 

 the trachytic. 



(4.) That the quartz rocks, of which some of the islands are 

 largely, and some entirely composed, are altered sandstones of Devo- 

 nian age, which clearly explains the occurrence of similar quartz 

 rocks on the Bosphorus, which are seen in the mountains of Bul- 

 gurlou and Tchemlidja, behind Scutari, and referred to by Mr. 

 Hamilton in his ' Observations on the Geology of Asia Minor.' 



Proceeding now with the descriptions, I shall take first the Island 

 of Prinkipo, and then follow on with the other islands in the order 

 of succession of the strata (and not according to their size), so as to 

 make, as nearly as possible, a continuous narrative. 



2. Island of Prlnlcipo. — This island is the largest in size of the 

 group, being about two miles and three quarters in extreme length 

 from IS'.E. to S.W., and about one mile in greatest breadth from E. 

 to W. The mountains of San Cristo and San George, rising respec- 

 tively to the heights of 450 and 650 feet above the level of the sea, 

 divide the island into two almost equal parts from the north to the 



* For the other communications read at this Evening -meeting, see Quart. 

 Journ. Geol. Soc. vol. xxiii. pp. 327 et seq. 



t Quart. Journ. Geol. Soc. vol. xx. p. 114. ' 



