Correspondence — Dr. J. 8. Flett. 569 



plant-petrifications, possibly of earlier age than the sandstones and 

 shales in which they occur. Two distinct and unmingled faunas 

 are present in the rocks : one consists of fi'esh-water Lamellibranchs, 

 and the other of marine fishes, Cephalopods, and Lamellibranchs ; 

 and the evidence as to horizon obtained from them agrees with 

 that yielded by the plant-remains. The paper concludes with a 

 bibliography. 



2. " The Titaniferous Basalts of the Western Mediterranean." 

 By Dr. Henry S. Washington, For. Corr. Geol. Soc. 



In 1905 the author visited the volcanic districts of Catalonia, 

 Sardinia, Pantelleria, and Linosa. He recognizes the existence in 

 this region of a hitherto unrecognized petrographic province, in 

 which the basalts contain a remarkably high percentage of titanium. 

 The rocks are of Tertiary age. Labradorite, augite, and olivine are 

 the essential minerals, with titaniferous magnetite and apatite, and 

 in some cases subordinate nepheline. The rocks vary from compact 

 to highly vesicular ; they are not conspicuously porphyritic, though 

 small phenocrysts of augite and olivine, and occasionally felspar, are 

 sometimes present. Olivine nodules occur in some cases. The 

 textures are those common in basalts, and ophitic relations are almost 

 wanting. A series of analyses is given ; the silica varies from 44 

 to 52 per cent,, the alumina from 12 to 19, and the titanium-oxide 

 from 2 to 5. The last oxide appears to be chiefly contained in 

 titaniferous magnetite. Phosphoric pentoxide is distinctly abundant, 

 and appears to vary, as the titanium does, with the amount of iron- 

 oxides. Soda is dominant ovei" potash in every instance. The 

 augites are almost, if not quite, colourless. The classification of the 

 rocks according to the quantitative system is discussed, and the 

 majority of the basalts fall into the ' Salfemane' class, the exceptions 

 being some of the Sardinian basalts and that of Graham's Island. 



The extent of the region is as yet problematical, and the author 

 points out that along the southern coast of France there are several 

 ' basaltic ' volcanoes, and it is possible that these may eventually 

 turn out to be connecting links between the rocks of Sardinia and 

 those of Catalonia, or possibly extrusion southwai'd is indicated by 

 the occurrence of phonolite at Maid Gharian, near Tripoli. 



coiRiRiBSDPOisriD-^nsrG:^. 



THE SOMABULA DIAMOND FIELD. 

 Sir, — Some months ago Sir John Wil lough by presented to the 

 Museum of Practical Geology a selection of minerals, accompanied 

 by photographs and plans, to illustrate the geology of the Rhodesian 

 diamond fields. These are now on exhibition on the main floor of 

 the Museum. It fell to my lot to determine the minerals, and as 

 the results are not exact!}'- the same as those obtained by Mr. Mennell 

 and given in his paper on the Somabula diamond field in the 

 October number of the Geological M.'^.gazine, I take the liberty of 

 sending you a few notes. 



