clxiv NOTES. 



of examining what would be the result given by a more satisfactory mode of 

 calculation under the most probable suppositions. Calculating under the two 

 hypotheses of the temperature of the air at the sea-shore having been either 

 27'5 cent, or 26'5 cent., and the height of the barometer reduced to the 

 freezing point 760 mm 0, he found, according to Regnault's Tables, that 77'5 

 cent, for the boiling point of water on the summit corresponds to a barometer 

 reading of 320 mm 20 at cent.;, the temperature of the air was + 17 cent., 

 which we may take for convenience as 1'5. According to these data, Oltmann's 

 tables give for the height attained, in the first hypothesis (27'5 cent.), 7328 ra 

 2, and in the second hypothesis (26'5 cent.), 7314 5, or, on the mean, 777 

 metres more than my trigonometric measurement. To have agreed with this 

 last, the experiment, supposing the summit of Chimborazo to have been really 

 attained, should have given the boiling point 2-25 cent, higher than it did. 

 (PoggendorfTs Annalen, Bd. 100, 1857, S. 479.) 



( 605 ) p. 433. As early as 1833, when placing the rich Sicilian collections of 

 Friedrich Hoffmann in the Berlin Mineralogical Cabinet, Gustav Kose satisfied 

 himself and his friends that the trachytes of Etna contain labradorite. In the 

 Memoir on the Eocks designated as greenstone and greenstone-porphyry (Pog- 

 gend. Ann. Bd. 34, 1835, S. 29), Gustav Rose mentions Etna lavas which 

 contain augite and labradorite* (Compare also Abich, in the fine Memoir on 

 the whole felspar family, 1840, in Poggend. Ann. Bd. 50, S. 347.) Leopold 

 von Buch calls the Etna-rock analogous to the dolerite of the Basalt formation. 

 (Poggend. Bd. 37, 1836, S. 188.) 



( 606 ) p. 433. Sartorius von Waltershausen, who has been for many years a 

 diligent explorer of the trachytes of Etna, makes the important remark: " That 

 hornblende there belongs rather to the older masses, the greenstone dikes in the 

 Val del Bove, and the white and reddish trachytes which form the base of Etna 

 in the Serra Giannicola. Black hornblendes and bright leek-green augites are 

 there found near together. The more recent lava-streams from 1 669 (particu- 

 larly those of 1787, 1809, 1811, 1819, 1832, 1838, and 1842) show augite, 

 but not hornblende, which appears to be produced under a slower rate of cool- 

 ing." (Waltershausen, Ueber die vulkani^chen Gesteine von Sicilien und Island, 

 1853, S. 11 1 114.) In the augite-containing trachytes of the Fourth Division, 

 in the chain of the Andes, I have found augite abundant, but in some cases 

 absolutely no crystals of hornblende, and in some others (as on Cotopaxi at an 

 elevation of 14,068 feet, and on Rucu Pichincha at an elevation of 15,304 feet) 

 a few interspersed rare but distinct black crystals of hornblende. 



( 8cr ) p. 433. Compare Pilla, in the Comptes rendus de 1'Acad. des Sc. 

 t. xx. 1845, p. 324. In the leucite-crystals of the Eocca Monfina, Pilla found 



