Washington — Contributions to Sardinian Petrography . 513 



Art. XXXII. — Contributions to Sardinian Petrography : I. 

 The Rocks of Monte Ferru ; by Henrv^ S. Washington. 



Introduction. — A considerable number of chemical analyses 

 have been made in past years of the igneous rocks of Sardinia 

 which were collected in 1905 and are still unpublished. As 

 there seems to be no immediate prospect of making the addi- 

 tional analyses needed for the rather complete study of Sar- 

 dinian lavas which was originally contemplated, it has been 

 decided to publish those already made, along with the proper 

 descriptive matter, so as to make them adequately available 

 to petrographers. The rocks of Monte Ferru will be first 

 described, then those of the recent small cones, and finally the 

 lavas of the early sheets. I have to thank Prof. J. V. Lewis 

 for the photographs of the trachyte. 



Monte Ferru. 



Bibliography. — The volcano of Monte Ferru was often men- 

 tioned and its main characters were well described (according 

 to the science of his day) in La Marmora's classic and monu- 

 mental work on Sardinia.* Twenty years later Doelter pub- 

 lished brief descriptions of its geologyf and lavas,;); with some 

 analyses and a geological map. 



Subsequently Bertolio§ gave a brief description of a few of 

 the rocks. The short notices of Zirkel and Rosenbusch appear 

 to have been based entirely on Doelter's work. The first 

 modern description of the volcano is found in two papers by 

 Dannenberg,|| who gives a geological map. In two more 

 recent papers T Deprat discusses very briefly the structure of 

 the volcano and the general chemical characters of its lavas, 

 though, unfortunately, he does not communicate the new 

 analyses which he made. The most important part of the vol- 

 cano is covered by the Santn Lussurgiu and Bosa sheets (Folio 

 206, III and IV)' of the Italian military map, scale 1:50,000. 



Topography and geology. — The volcano of Monte Ferru is 

 situated at about the center of the west coast of Sardinia, mid- 

 way between the towns of Bosa on the north and Oristano on 

 the south and 40 km. north of Monte Arci. The area cov- 

 ered by its lava is at least 700 square kilometers. Its greatest 



*A. de La Marmora, Voyage en Sardaigne, Description Geologique, 2 

 vols., Turin, 1857. 



fC. Doelter, Denkschr. Ak. Wiss. Wien, xxxviii, p. 193, 1877. 



JC. Doelter, op. cit., xxxix, p. 41, 1878. 



§S. Bertolio, Boll. Com. Geol. Ital.. 1896, p. 190. 



I A. Dannenberg, Sb. Prens. Ak. Wiss., 1903, p. 853; Neues Jahrb., Beil. 

 Bd., xxi, p. 1,1905. 



IT J. Deprat, C. R., cxlv, p. 820, 1907 ; C. R, cxlvi, p. 702, 1908. 



