390 NOTES ON THE GEOLOGY 



acute rlioinboids. Their acute trihedral summits are sometimes 

 replaced by a much more obtuse trihedral summit, forming a 

 doubly trihedral termination. But it is difficult to give a definite 

 idea of these crystals without figures. Those with simple trihe- 

 dral summits correspond nearly to Figs. 101, 106, and 108, of 

 Shepard's Mineralogy, Vol. I. p. 99, 100, But I havc^ found it 

 impossible to measure the obliquity of the rhomboid, because 

 only the terminating pyramid projects from the surface. 



No. 241 is a small stalactite formed at Broosa by water drip- 

 ping from an aqueduct. It is scarcely at all crystalline, but con- 

 sists of thin successive cylinders of soft limestone enveloping one 

 another, and apparently cohering so little that one might be 

 slipped out of the other, were they not somewhat UTCgiilar. 



Nos. 176, 177, 184, and 185, were obtained by Messrs. Schnei- 

 der and Powers, on an excursion from Broosa to Kutaieh. They 

 appear to be metamorphic slates, and indicate the powerful action 

 of heat. No. 171 appears, also, to be metamorphic, and contains 

 a large per centum of red oxide of iron. No. 170 is a beautiful 

 mixture of red and white opal, from the plain of Kutaieh, near a 

 ridge of the Taurus. 



Nos. 178 and 295 are vesicular lava from the Katakekaumene, 

 or Burnt District of the Greeks, described by Strabo, It lies 

 east of Smyrna, near the ancient Philadelphia. Mr. Schneider 

 says, "these black stones extend over a distance of twenty or 

 thirty miles, and the whole has the appearance of a stream of 

 lava, not very wide, suddenly cooled." No. 362 is compact lava 

 from the same district, sent me by Mr. Homes.* 



In 1841 Mr. Van Lennep took an excursion by land through 

 a part of Asia Minor, thence across the Sea of JMarmora into Rou- 

 melia, as far, I believe, as Adrianople. His account of the rocks 

 of Mount Olympus and northerly to the lake of Nice, has already 

 been presented. Some additional facts will now be given. 



* Mr. M'. J. Hamilton, in a paper read two or three years ago to the London Geologi- 

 cal Society, describes three periods of eruption in the Katakekaumene, all of them pre- 

 vious to historical dates. (Dr. BvcKhAyu'S Anniversary Address before the Geological 

 Society, February, 1840, p. 37.) 



