NOTES. Clxv 



the surface covered with worm-tubes (serpulese), which indicates submarine 

 volcanic origin. On the leucite-rock of the Eifel in the trachyte of the Burg- 

 berg near Rieden, and that of Albano, Lago Bracciano and Borghetto, north of 

 Rome, see Kosmos, Bd. iv. S. 32, Anm. 93 (English edition, Note 317). In 

 the centre of a large crystal of leucite, Leopold von Buch has often found the 

 fragment of a crystal of augite, around which the leucitic crystallisation has 

 taken place, "which, as has been already remarked, seems somewhat strange, 

 viewing the easy fusibility of augite and the non-fusibility of leucite. It is still 

 more frequent to find pieces of the paste of the leucite-porphyry itself enclosed 

 as a nucleus." Olivine is also found in lavas: as in the cavities of the obsidian 

 which I brought from Mexico from the Cerro del Jacal (Kosmos, Bd. i. S. 464, 

 Anm. 60); and yet it is also found in the hypersthene-rock of Elfdal, which 

 was long taken for syenite. (Berzelius, Sechster Jahresbericht, 1827, S. 302.) 

 Oligoclase presents a similar contrast in respect to the places in which it is 

 found: it occurs in the trachytes of still burning volcanoes (Peak of Teneriffe 

 and Cotopaxi) ; and yet it presents itself also in the granite and granitite of 

 Schreibersau and Warmbrunn in the Silesian Riesengebirge. (Gustav Rose, On 

 the Rocks belonging to the Granite Group, in the Zeitschrift der deutschen geol. 

 Gesellschaft zu Berlin, Bd. i. S. 364.) It is not so with leucite in Plutonic 

 rocks ; for the statement that leucites are found interspersed in the mica-slate 

 and gneiss of the Pyrenees at Gavarnie (which has even been repeated by Hauy), 

 has been found by Dufre'noy, by several years of local examination, to be erro- 

 neous. (Traite' de Mine'ralogie, t. iii. p. 399.) 



( 608 ) p. 435. In a geological journey, which I made in 1795, through the 

 south of France, the west of Switzerland, and the north of Italy, I had been 

 convinced that the Jurassic limestone which Werner reckoned as belonging to 

 his Muschelkalk, constituted a distinct formation. In my memoir on subterra- 

 nean gases, which my brother, Wilhelm von Humboldt, published in 1799, while 

 I was in South America, this formation, which I had designated provisionally as 

 Jura limestone, was first mentioned (S. 39). It was thence immediately adopted 

 into Oberbergrath Karsten's " Mineralogische Tabellen," which were then much 

 read. (1800, S. 64, and Vorrede, S. vii.) I had not named any of the fossils 

 which characterise the formation, and respecting which Leopold von Buch did 

 such valuable service in 1 839 ; I was also mistaken in the age which I assigned 

 to it, as from the neighbourhood of the Alps, which were then believed to be 

 older than Zechstein, I supposed it to be older than the Muschelkalk. In the 

 earliest Tables of Buckland, " On the Superposition of Strata in the British 

 Islands," the " Jura-limestone " of Humboldt is reckoned as belonging to the 



