THE ANALCITE BASALTS OF SARDINIA 



H. S. WASHINGTON 

 Geophysical Laboratory, Carnegie Institution of Washington 



Introduction. — ^In his well-known paper^ entitled "Die Producte 

 des Vulcans Monte Ferru," Doelter first noted the presence of 

 "leucite basalts" at this volcano, as well as near Pozzo Maggiore, 

 giving a brief description and an analysis. Later, Dannenberg^ and 

 Deprat^ confirmed the occurrence of leucite rocks at Ferru, and 

 showed that these flows belong to the closing period of volcanic 

 activity. In the autumn of 1905 I visited Sardinia for the Car- 

 negie Institution of Washington, making a special study of the 

 different volcanoes of this island. Although my observations were 

 necessarily brief, I was able to confirm the opinion of these geolo- 

 gists. The first analysis, which I made some years ago, of a speci- 

 men from Scano gave such unexpected results as regards the alkalies 

 that I made two others of these so-called leucite rocks from other 

 localities. All three were in harmony. Since these rocks have 

 always been considered to be and have been cited as being leucitic, 

 although in reality the so-called leucite is analcite, it seemed to me 

 that a special note would be of interest. The lavas of Monte Ferru 

 and of the other Sardinian volcanoes will be described in other 

 papers. 



I have to thank my friends. Professor J. V. Lewis for the photo- 

 graphs of the thin sections, and Doctors F. E. Wright and H. E. 

 Merwin of the Geophysical Laboratory for the optical study of the 

 analcite and biotite. 



Occurrence. — Although these basalts vary somewhat in their 

 modal characters, yet they are so closely allied that they may well 

 be described together. One prominent locality, already noted by 

 Doelter,'' is a massive flow, from 6 to 10 m. thick, on the other 



^ C. Doelter, Denks. Akad. Wiss. Wien, XXXIX (1878), 41. 

 = A. Dannenberg, Neu. Jahrh., Beil^. Bd., XXI (1905), 48. 

 3 G. Deprat, C.R., CLV (1907), 823. -» C. Doelter, op. cit., p. 78. 



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